Indexed rendering. Not in main branch because breaks rendering code too much. Will merge in trunk along with more major graphics changes lat

examples/directx11_example/imgui_impl_dx11.cpp

@@ -18,6 +18,7 @@ static HWND                     g_hWnd = 0;
 static ID3D11Device*            g_pd3dDevice = NULL;
 static ID3D11DeviceContext*     g_pd3dDeviceContext = NULL;
 static ID3D11Buffer*            g_pVB = NULL;
+static ID3D11Buffer*            g_pIB = NULL;
 static ID3D10Blob *             g_pVertexShaderBlob = NULL;
 static ID3D11VertexShader*      g_pVertexShader = NULL;
 static ID3D11InputLayout*       g_pInputLayout = NULL;
@@ -27,7 +28,8 @@ static ID3D11PixelShader*       g_pPixelShader = NULL;
 static ID3D11SamplerState*      g_pFontSampler = NULL;
 static ID3D11ShaderResourceView*g_pFontTextureView = NULL;
 static ID3D11BlendState*        g_blendState = NULL;
-static int                      VERTEX_BUFFER_SIZE = 30000;     // TODO: Make vertex buffer smaller and grow dynamically as needed.
+static int                      VERTEX_BUFFER_SIZE = 30000;     // TODO: Make buffers smaller and grow dynamically as needed.
+static int                      INDEX_BUFFER_SIZE = 30000;      // TODO: Make buffers smaller and grow dynamically as needed.
 
 struct CUSTOMVERTEX
 {
@@ -47,10 +49,13 @@ struct VERTEX_CONSTANT_BUFFER
 static void ImGui_ImplDX11_RenderDrawLists(ImDrawList** const cmd_lists, int cmd_lists_count)
 {
     // Copy and convert all vertices into a single contiguous buffer
-    D3D11_MAPPED_SUBRESOURCE mappedResource;
-    if (g_pd3dDeviceContext->Map(g_pVB, 0, D3D11_MAP_WRITE_DISCARD, 0, &mappedResource) != S_OK)
+    D3D11_MAPPED_SUBRESOURCE vtx_resource, idx_resource;
+    if (g_pd3dDeviceContext->Map(g_pVB, 0, D3D11_MAP_WRITE_DISCARD, 0, &vtx_resource) != S_OK)
         return;
-    CUSTOMVERTEX* vtx_dst = (CUSTOMVERTEX*)mappedResource.pData;
+    if (g_pd3dDeviceContext->Map(g_pIB, 0, D3D11_MAP_WRITE_DISCARD, 0, &idx_resource) != S_OK)
+        return;
+    CUSTOMVERTEX* vtx_dst = (CUSTOMVERTEX*)vtx_resource.pData;
+    ImDrawIdx* idx_dst = (ImDrawIdx*)idx_resource.pData;
     for (int n = 0; n < cmd_lists_count; n++)
     {
         const ImDrawList* cmd_list = cmd_lists[n];
@@ -65,8 +70,11 @@ static void ImGui_ImplDX11_RenderDrawLists(ImDrawList** const cmd_lists, int cmd
             vtx_dst++;
             vtx_src++;
         }
+        memcpy(idx_dst, &cmd_list->idx_buffer[0], cmd_list->idx_buffer.size() * sizeof(ImDrawIdx));
+        idx_dst += cmd_list->idx_buffer.size();
     }
     g_pd3dDeviceContext->Unmap(g_pVB, 0);
+    g_pd3dDeviceContext->Unmap(g_pIB, 0);
 
     // Setup orthographic projection matrix into our constant buffer
     {
@@ -108,6 +116,7 @@ static void ImGui_ImplDX11_RenderDrawLists(ImDrawList** const cmd_lists, int cmd
     unsigned int offset = 0;
     g_pd3dDeviceContext->IASetInputLayout(g_pInputLayout);
     g_pd3dDeviceContext->IASetVertexBuffers(0, 1, &g_pVB, &stride, &offset);
+    g_pd3dDeviceContext->IASetIndexBuffer(g_pIB, DXGI_FORMAT_R16_UINT, 0);
     g_pd3dDeviceContext->IASetPrimitiveTopology(D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
     g_pd3dDeviceContext->VSSetShader(g_pVertexShader, NULL, 0);
     g_pd3dDeviceContext->VSSetConstantBuffers(0, 1, &g_pVertexConstantBuffer);
@@ -120,6 +129,7 @@ static void ImGui_ImplDX11_RenderDrawLists(ImDrawList** const cmd_lists, int cmd
 
     // Render command lists
     int vtx_offset = 0;
+    int idx_offset = 0;
     for (int n = 0; n < cmd_lists_count; n++)
     {
         const ImDrawList* cmd_list = cmd_lists[n];
@@ -135,10 +145,11 @@ static void ImGui_ImplDX11_RenderDrawLists(ImDrawList** const cmd_lists, int cmd
                 const D3D11_RECT r = { (LONG)pcmd->clip_rect.x, (LONG)pcmd->clip_rect.y, (LONG)pcmd->clip_rect.z, (LONG)pcmd->clip_rect.w };
                 g_pd3dDeviceContext->PSSetShaderResources(0, 1, (ID3D11ShaderResourceView**)&pcmd->texture_id);
                 g_pd3dDeviceContext->RSSetScissorRects(1, &r); 
-                g_pd3dDeviceContext->Draw(pcmd->vtx_count, vtx_offset);
+                g_pd3dDeviceContext->DrawIndexed(pcmd->idx_count, idx_offset, vtx_offset);
             }
-            vtx_offset += pcmd->vtx_count;
+            idx_offset += pcmd->idx_count;
         }
+        vtx_offset += cmd_list->vtx_buffer.size();
     }
 
     // Restore modified state
@@ -362,11 +373,22 @@ bool    ImGui_ImplDX11_CreateDeviceObjects()
         bufferDesc.ByteWidth = VERTEX_BUFFER_SIZE * sizeof(CUSTOMVERTEX);
         bufferDesc.BindFlags = D3D11_BIND_VERTEX_BUFFER;
         bufferDesc.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;
-        bufferDesc.MiscFlags = 0;
         if (g_pd3dDevice->CreateBuffer(&bufferDesc, NULL, &g_pVB) < 0)
             return false;
     }
 
+    // Create the index buffer
+    {
+        D3D11_BUFFER_DESC bufferDesc;
+        memset(&bufferDesc, 0, sizeof(D3D11_BUFFER_DESC));
+        bufferDesc.Usage = D3D11_USAGE_DYNAMIC;
+        bufferDesc.ByteWidth = INDEX_BUFFER_SIZE * sizeof(ImDrawIdx);
+        bufferDesc.BindFlags = D3D11_BIND_INDEX_BUFFER;
+        bufferDesc.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;
+        if (g_pd3dDevice->CreateBuffer(&bufferDesc, NULL, &g_pIB) < 0)
+            return false;
+    }
+
     ImGui_ImplDX11_CreateFontsTexture();
 
     return true;
@@ -379,6 +401,7 @@ void    ImGui_ImplDX11_InvalidateDeviceObjects()
 
     if (g_pFontSampler) { g_pFontSampler->Release(); g_pFontSampler = NULL; }
     if (g_pFontTextureView) { g_pFontTextureView->Release(); ImGui::GetIO().Fonts->TexID = 0; }
+    if (g_pIB) { g_pIB->Release(); g_pIB = NULL; }
     if (g_pVB) { g_pVB->Release(); g_pVB = NULL; }
 
     if (g_blendState) { g_blendState->Release(); g_blendState = NULL; }

examples/directx9_example/imgui_impl_dx9.cpp

@@ -15,7 +15,9 @@ static INT64                    g_Time = 0;
 static INT64                    g_TicksPerSecond = 0;
 static LPDIRECT3DDEVICE9        g_pd3dDevice = NULL;
 static LPDIRECT3DVERTEXBUFFER9  g_pVB = NULL;
-static int                      VERTEX_BUFFER_SIZE = 30000;     // TODO: Make vertex buffer smaller and grow dynamically as needed.
+static LPDIRECT3DINDEXBUFFER9   g_pIB = NULL;
+static int                      VERTEX_BUFFER_SIZE = 30000;     // TODO: Make buffers smaller and grow dynamically as needed.
+static int                      INDEX_BUFFER_SIZE = 30000;      // TODO: Make buffers smaller and grow dynamically as needed.
 
 struct CUSTOMVERTEX
 {
@@ -31,15 +33,22 @@ struct CUSTOMVERTEX
 static void ImGui_ImplDX9_RenderDrawLists(ImDrawList** const cmd_lists, int cmd_lists_count)
 {
     size_t total_vtx_count = 0;
+    size_t total_idx_count = 0;
     for (int n = 0; n < cmd_lists_count; n++)
+    {
         total_vtx_count += cmd_lists[n]->vtx_buffer.size();
+        total_idx_count += cmd_lists[n]->idx_buffer.size();
+    }
     if (total_vtx_count == 0)
         return;
 
     // Copy and convert all vertices into a single contiguous buffer
     CUSTOMVERTEX* vtx_dst;
+    ImDrawIdx* idx_dst;
     if (g_pVB->Lock(0, (UINT)total_vtx_count, (void**)&vtx_dst, D3DLOCK_DISCARD) < 0)
         return;
+    if (g_pIB->Lock(0, (UINT)total_idx_count, (void**)&idx_dst, D3DLOCK_DISCARD) < 0)
+        return;
     for (int n = 0; n < cmd_lists_count; n++)
     {
         const ImDrawList* cmd_list = cmd_lists[n];
@@ -55,9 +64,13 @@ static void ImGui_ImplDX9_RenderDrawLists(ImDrawList** const cmd_lists, int cmd_
             vtx_dst++;
             vtx_src++;
         }
+        memcpy(idx_dst, &cmd_list->idx_buffer[0], cmd_list->idx_buffer.size() * sizeof(ImDrawIdx));
+        idx_dst += cmd_list->idx_buffer.size();
     }
     g_pVB->Unlock();
+    g_pIB->Unlock();
     g_pd3dDevice->SetStreamSource( 0, g_pVB, 0, sizeof( CUSTOMVERTEX ) );
+    g_pd3dDevice->SetIndices( g_pIB );
     g_pd3dDevice->SetFVF( D3DFVF_CUSTOMVERTEX );
 
     // Setup render state: fixed-pipeline, alpha-blending, no face culling, no depth testing
@@ -90,6 +103,7 @@ static void ImGui_ImplDX9_RenderDrawLists(ImDrawList** const cmd_lists, int cmd_
 
     // Render command lists
     int vtx_offset = 0;
+    int idx_offset = 0;
     for (int n = 0; n < cmd_lists_count; n++)
     {
         const ImDrawList* cmd_list = cmd_lists[n];
@@ -105,10 +119,11 @@ static void ImGui_ImplDX9_RenderDrawLists(ImDrawList** const cmd_lists, int cmd_
                 const RECT r = { (LONG)pcmd->clip_rect.x, (LONG)pcmd->clip_rect.y, (LONG)pcmd->clip_rect.z, (LONG)pcmd->clip_rect.w };
                 g_pd3dDevice->SetTexture( 0, (LPDIRECT3DTEXTURE9)pcmd->texture_id );
                 g_pd3dDevice->SetScissorRect(&r);
-                g_pd3dDevice->DrawPrimitive(D3DPT_TRIANGLELIST, vtx_offset, pcmd->vtx_count/3);
+                g_pd3dDevice->DrawIndexedPrimitive(D3DPT_TRIANGLELIST, vtx_offset, 0, cmd_list->vtx_buffer.size(), idx_offset, pcmd->idx_count/3);
             }
-            vtx_offset += pcmd->vtx_count;
+            idx_offset += pcmd->idx_count;
         }
+        vtx_offset += cmd_list->vtx_buffer.size();
     }
 }
 
@@ -234,6 +249,9 @@ bool ImGui_ImplDX9_CreateDeviceObjects()
     if (g_pd3dDevice->CreateVertexBuffer(VERTEX_BUFFER_SIZE * sizeof(CUSTOMVERTEX), D3DUSAGE_DYNAMIC | D3DUSAGE_WRITEONLY, D3DFVF_CUSTOMVERTEX, D3DPOOL_DEFAULT, &g_pVB, NULL) < 0)
         return false;
 
+    if (g_pd3dDevice->CreateIndexBuffer(INDEX_BUFFER_SIZE * sizeof(ImDrawIdx), D3DUSAGE_DYNAMIC | D3DUSAGE_WRITEONLY, D3DFMT_INDEX16, D3DPOOL_DEFAULT, &g_pIB, NULL) < 0)
+        return false;
+
     ImGui_ImplDX9_CreateFontsTexture();
     return true;
 }
@@ -247,6 +265,11 @@ void ImGui_ImplDX9_InvalidateDeviceObjects()
         g_pVB->Release();
         g_pVB = NULL;
     }
+    if (g_pIB)
+    {
+        g_pIB->Release();
+        g_pIB = NULL;
+    }
     if (LPDIRECT3DTEXTURE9 tex = (LPDIRECT3DTEXTURE9)ImGui::GetIO().Fonts->TexID)
     {
         tex->Release();

examples/opengl3_example/imgui_impl_glfw_gl3.cpp

@@ -23,7 +23,7 @@ static GLuint       g_FontTexture = 0;
 static int          g_ShaderHandle = 0, g_VertHandle = 0, g_FragHandle = 0;
 static int          g_AttribLocationTex = 0, g_AttribLocationProjMtx = 0;
 static int          g_AttribLocationPosition = 0, g_AttribLocationUV = 0, g_AttribLocationColor = 0;
-static size_t       g_VboMaxSize = 20000;
+static size_t       g_VboSize = 0;
 static unsigned int g_VboHandle = 0, g_VaoHandle = 0;
 
 // This is the main rendering function that you have to implement and provide to ImGui (via setting up 'RenderDrawListsFn' in the ImGuiIO structure)
@@ -62,32 +62,33 @@ static void ImGui_ImplGlfwGL3_RenderDrawLists(ImDrawList** const cmd_lists, int
     for (int n = 0; n < cmd_lists_count; n++)
         total_vtx_count += cmd_lists[n]->vtx_buffer.size();
     glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
-    size_t neededBufferSize = total_vtx_count * sizeof(ImDrawVert);
-    if (neededBufferSize > g_VboMaxSize)
+    size_t needed_vtx_size = total_vtx_count * sizeof(ImDrawVert);
+    if (g_VboSize < needed_vtx_size)
     {
-        g_VboMaxSize = neededBufferSize + 5000;  // Grow buffer
-        glBufferData(GL_ARRAY_BUFFER, g_VboMaxSize, NULL, GL_STREAM_DRAW);
+        g_VboSize = needed_vtx_size + 8192;  // Grow buffer
+        glBufferData(GL_ARRAY_BUFFER, g_VboSize, NULL, GL_STREAM_DRAW);
     }
 
     // Copy and convert all vertices into a single contiguous buffer
-    unsigned char* buffer_data = (unsigned char*)glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY);
-    if (!buffer_data)
+    unsigned char* vtx_data = (unsigned char*)glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY);
+    if (!vtx_data)
         return;
     for (int n = 0; n < cmd_lists_count; n++)
     {
         const ImDrawList* cmd_list = cmd_lists[n];
-        memcpy(buffer_data, &cmd_list->vtx_buffer[0], cmd_list->vtx_buffer.size() * sizeof(ImDrawVert));
-        buffer_data += cmd_list->vtx_buffer.size() * sizeof(ImDrawVert);
+        memcpy(vtx_data, &cmd_list->vtx_buffer[0], cmd_list->vtx_buffer.size() * sizeof(ImDrawVert));
+        vtx_data += cmd_list->vtx_buffer.size() * sizeof(ImDrawVert);
     }
     glUnmapBuffer(GL_ARRAY_BUFFER);
     glBindBuffer(GL_ARRAY_BUFFER, 0);
     glBindVertexArray(g_VaoHandle);
 
-    int cmd_offset = 0;
+    int vtx_offset = 0;
     for (int n = 0; n < cmd_lists_count; n++)
     {
         const ImDrawList* cmd_list = cmd_lists[n];
-        int vtx_offset = cmd_offset;
+        const ImDrawIdx* idx_buffer = (const unsigned short*)&cmd_list->idx_buffer.front();
+
         const ImDrawCmd* pcmd_end = cmd_list->commands.end();
         for (const ImDrawCmd* pcmd = cmd_list->commands.begin(); pcmd != pcmd_end; pcmd++)
         {
@@ -99,11 +100,11 @@ static void ImGui_ImplGlfwGL3_RenderDrawLists(ImDrawList** const cmd_lists, int
             {
                 glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->texture_id);
                 glScissor((int)pcmd->clip_rect.x, (int)(height - pcmd->clip_rect.w), (int)(pcmd->clip_rect.z - pcmd->clip_rect.x), (int)(pcmd->clip_rect.w - pcmd->clip_rect.y));
-                glDrawArrays(GL_TRIANGLES, vtx_offset, pcmd->vtx_count);
+                glDrawElementsBaseVertex(GL_TRIANGLES, pcmd->idx_count, GL_UNSIGNED_SHORT, idx_buffer, vtx_offset);
             }
-            vtx_offset += pcmd->vtx_count;
+            idx_buffer += pcmd->idx_count;
         }
-        cmd_offset = vtx_offset;
+        vtx_offset += cmd_list->vtx_buffer.size();
     }
 
     // Restore modified state
@@ -217,8 +218,6 @@ bool ImGui_ImplGlfwGL3_CreateDeviceObjects()
     g_AttribLocationColor = glGetAttribLocation(g_ShaderHandle, "Color");
 
     glGenBuffers(1, &g_VboHandle);
-    glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
-    glBufferData(GL_ARRAY_BUFFER, g_VboMaxSize, NULL, GL_DYNAMIC_DRAW);
 
     glGenVertexArrays(1, &g_VaoHandle);
     glBindVertexArray(g_VaoHandle);

examples/opengl_example/imgui_impl_glfw.cpp

@@ -60,11 +60,11 @@ static void ImGui_ImplGlfw_RenderDrawLists(ImDrawList** const cmd_lists, int cmd
     {
         const ImDrawList* cmd_list = cmd_lists[n];
         const unsigned char* vtx_buffer = (const unsigned char*)&cmd_list->vtx_buffer.front();
+        const ImDrawIdx* idx_buffer = (const unsigned short*)&cmd_list->idx_buffer.front();
         glVertexPointer(2, GL_FLOAT, sizeof(ImDrawVert), (void*)(vtx_buffer + OFFSETOF(ImDrawVert, pos)));
         glTexCoordPointer(2, GL_FLOAT, sizeof(ImDrawVert), (void*)(vtx_buffer + OFFSETOF(ImDrawVert, uv)));
         glColorPointer(4, GL_UNSIGNED_BYTE, sizeof(ImDrawVert), (void*)(vtx_buffer + OFFSETOF(ImDrawVert, col)));
 
-        int vtx_offset = 0;
         for (size_t cmd_i = 0; cmd_i < cmd_list->commands.size(); cmd_i++)
         {
             const ImDrawCmd* pcmd = &cmd_list->commands[cmd_i];
@@ -76,9 +76,9 @@ static void ImGui_ImplGlfw_RenderDrawLists(ImDrawList** const cmd_lists, int cmd
             {
                 glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->texture_id);
                 glScissor((int)pcmd->clip_rect.x, (int)(height - pcmd->clip_rect.w), (int)(pcmd->clip_rect.z - pcmd->clip_rect.x), (int)(pcmd->clip_rect.w - pcmd->clip_rect.y));
-                glDrawArrays(GL_TRIANGLES, vtx_offset, pcmd->vtx_count);
+                glDrawElements(GL_TRIANGLES, pcmd->idx_count, GL_UNSIGNED_SHORT, idx_buffer);
             }
-            vtx_offset += pcmd->vtx_count;
+            idx_buffer += pcmd->idx_count;
         }
     }
     #undef OFFSETOF

imgui.cpp

@@ -1670,10 +1670,11 @@ static inline void AddDrawListToRenderList(ImVector<ImDrawList*>& out_render_lis
 {
     if (!draw_list->commands.empty() && !draw_list->vtx_buffer.empty())
     {
-        if (draw_list->commands.back().vtx_count == 0)
+        if (draw_list->commands.back().idx_count == 0)
             draw_list->commands.pop_back();
         out_render_list.push_back(draw_list);
         GImGui->IO.MetricsRenderVertices += (int)draw_list->vtx_buffer.size();
+        GImGui->IO.MetricsRenderIndices += (int)draw_list->idx_buffer.size();
     }
 }
 
@@ -2207,7 +2208,7 @@ void ImGui::Render()
         }
 
         // Gather windows to render
-        g.IO.MetricsRenderVertices = 0;
+        g.IO.MetricsRenderVertices = g.IO.MetricsRenderIndices = 0;
         for (size_t i = 0; i < IM_ARRAYSIZE(g.RenderDrawLists); i++)
             g.RenderDrawLists[i].resize(0);
         for (size_t i = 0; i != g.Windows.size(); i++)
@@ -7590,6 +7591,9 @@ void ImDrawList::Clear()
     commands.resize(0);
     vtx_buffer.resize(0);
     vtx_write = NULL;
+    vtx_current_idx = 0;
+    idx_buffer.resize(0);
+    idx_write = NULL;
     clip_rect_stack.resize(0);
     texture_id_stack.resize(0);
 }
@@ -7599,6 +7603,9 @@ void ImDrawList::ClearFreeMemory()
     commands.clear();
     vtx_buffer.clear();
     vtx_write = NULL;
+    vtx_current_idx = 0;
+    idx_buffer.clear();
+    idx_write = NULL;
     clip_rect_stack.clear();
     texture_id_stack.clear();
 }
@@ -7606,7 +7613,7 @@ void ImDrawList::ClearFreeMemory()
 void ImDrawList::AddDrawCmd()
 {
     ImDrawCmd draw_cmd;
-    draw_cmd.vtx_count = 0;
+    draw_cmd.idx_count = 0;
     draw_cmd.clip_rect = clip_rect_stack.empty() ? GNullClipRect : clip_rect_stack.back();
     draw_cmd.texture_id = texture_id_stack.empty() ? NULL : texture_id_stack.back();
     draw_cmd.user_callback = NULL;
@@ -7619,7 +7626,7 @@ void ImDrawList::AddDrawCmd()
 void ImDrawList::AddCallback(ImDrawCallback callback, void* callback_data)
 {
     ImDrawCmd* current_cmd = commands.empty() ? NULL : &commands.back();
-    if (!current_cmd || current_cmd->vtx_count != 0 || current_cmd->user_callback != NULL)
+    if (!current_cmd || current_cmd->idx_count != 0 || current_cmd->user_callback != NULL)
     {
         AddDrawCmd();
         current_cmd = &commands.back();
@@ -7635,7 +7642,7 @@ void ImDrawList::AddCallback(ImDrawCallback callback, void* callback_data)
 void ImDrawList::UpdateClipRect()
 {
     ImDrawCmd* current_cmd = commands.empty() ? NULL : &commands.back();
-    if (!current_cmd || (current_cmd->vtx_count != 0) || current_cmd->user_callback != NULL)
+    if (!current_cmd || (current_cmd->idx_count != 0) || current_cmd->user_callback != NULL)
     {
         AddDrawCmd();
     }
@@ -7675,7 +7682,7 @@ void ImDrawList::UpdateTextureID()
 {
     ImDrawCmd* current_cmd = commands.empty() ? NULL : &commands.back();
     const ImTextureID texture_id = texture_id_stack.empty() ? NULL : texture_id_stack.back();
-    if (!current_cmd || (current_cmd->vtx_count != 0 && current_cmd->texture_id != texture_id) || current_cmd->user_callback != NULL)
+    if (!current_cmd || (current_cmd->idx_count != 0 && current_cmd->texture_id != texture_id) || current_cmd->user_callback != NULL)
     {
         AddDrawCmd();
     }
@@ -7698,23 +7705,30 @@ void ImDrawList::PopTextureID()
     UpdateTextureID();
 }
 
-void ImDrawList::PrimReserve(unsigned int vtx_count)
+void ImDrawList::PrimReserve(unsigned int idx_count, unsigned int vtx_count)
 {
     ImDrawCmd& draw_cmd = commands.back();
-    draw_cmd.vtx_count += vtx_count;
-
+    draw_cmd.idx_count += idx_count;
+        
     size_t vtx_buffer_size = vtx_buffer.size();
     vtx_buffer.resize(vtx_buffer_size + vtx_count);
     vtx_write = &vtx_buffer[vtx_buffer_size];
+
+    size_t idx_buffer_size = idx_buffer.size();
+    idx_buffer.resize(idx_buffer_size + idx_count);
+    idx_write = &idx_buffer[idx_buffer_size];
 }
 
 void ImDrawList::PrimTriangle(const ImVec2& a, const ImVec2& b, const ImVec2& c, ImU32 col)
 {
     const ImVec2 uv = GImGui->FontTexUvWhitePixel;
-    vtx_write[0].pos = a; vtx_write[0].uv = uv; vtx_write[0].col = col;
-    vtx_write[1].pos = b; vtx_write[1].uv = uv; vtx_write[1].col = col;
-    vtx_write[2].pos = c; vtx_write[2].uv = uv; vtx_write[2].col = col;
+    idx_write[0] = vtx_current_idx; idx_write[1] = vtx_current_idx+1; idx_write[2] = vtx_current_idx+2; 
+    vtx_write[0].pos = a; vtx_write[0].uv = uv; vtx_write[0].col = col; 
+    vtx_write[1].pos = b; vtx_write[1].uv = uv; vtx_write[1].col = col; 
+    vtx_write[2].pos = c; vtx_write[2].uv = uv; vtx_write[2].col = col; 
     vtx_write += 3;
+    vtx_current_idx += 3;
+    idx_write += 3;
 }
 
 void ImDrawList::PrimRect(const ImVec2& a, const ImVec2& c, ImU32 col)
@@ -7722,13 +7736,15 @@ void ImDrawList::PrimRect(const ImVec2& a, const ImVec2& c, ImU32 col)
     const ImVec2 uv = GImGui->FontTexUvWhitePixel;
 	const ImVec2 b(c.x, a.y);
 	const ImVec2 d(a.x, c.y);
-    vtx_write[0].pos = a; vtx_write[0].uv = uv; vtx_write[0].col = col;
-    vtx_write[1].pos = b; vtx_write[1].uv = uv; vtx_write[1].col = col;
-    vtx_write[2].pos = c; vtx_write[2].uv = uv; vtx_write[2].col = col;
-    vtx_write[3].pos = a; vtx_write[3].uv = uv; vtx_write[3].col = col;
-    vtx_write[4].pos = c; vtx_write[4].uv = uv; vtx_write[4].col = col;
-    vtx_write[5].pos = d; vtx_write[5].uv = uv; vtx_write[5].col = col;
-    vtx_write += 6;
+    idx_write[0] = vtx_current_idx; idx_write[1] = vtx_current_idx+1; idx_write[2] = vtx_current_idx+2; 
+    idx_write[3] = vtx_current_idx; idx_write[4] = vtx_current_idx+2; idx_write[5] = vtx_current_idx+3; 
+    vtx_write[0].pos = a; vtx_write[0].uv = uv; vtx_write[0].col = col; 
+    vtx_write[1].pos = b; vtx_write[1].uv = uv; vtx_write[1].col = col; 
+    vtx_write[2].pos = c; vtx_write[2].uv = uv; vtx_write[2].col = col; 
+    vtx_write[3].pos = d; vtx_write[3].uv = uv; vtx_write[3].col = col;
+    vtx_write += 4;
+    vtx_current_idx += 4;
+    idx_write += 6;
 }
 
 void ImDrawList::PrimRectUV(const ImVec2& a, const ImVec2& c, const ImVec2& uv_a, const ImVec2& uv_c, ImU32 col)
@@ -7737,25 +7753,29 @@ void ImDrawList::PrimRectUV(const ImVec2& a, const ImVec2& c, const ImVec2& uv_a
 	const ImVec2 d(a.x, c.y);
 	const ImVec2 uv_b(uv_c.x, uv_a.y);
 	const ImVec2 uv_d(uv_a.x, uv_c.y);
-    vtx_write[0].pos = a; vtx_write[0].uv = uv_a; vtx_write[0].col = col;
-    vtx_write[1].pos = b; vtx_write[1].uv = uv_b; vtx_write[1].col = col;
-    vtx_write[2].pos = c; vtx_write[2].uv = uv_c; vtx_write[2].col = col;
-    vtx_write[3].pos = a; vtx_write[3].uv = uv_a; vtx_write[3].col = col;
-    vtx_write[4].pos = c; vtx_write[4].uv = uv_c; vtx_write[4].col = col;
-    vtx_write[5].pos = d; vtx_write[5].uv = uv_d; vtx_write[5].col = col;
-    vtx_write += 6;
+    idx_write[0] = vtx_current_idx; idx_write[1] = vtx_current_idx+1; idx_write[2] = vtx_current_idx+2; 
+    idx_write[3] = vtx_current_idx; idx_write[4] = vtx_current_idx+2; idx_write[5] = vtx_current_idx+3; 
+    vtx_write[0].pos = a; vtx_write[0].uv = uv_a; vtx_write[0].col = col; 
+    vtx_write[1].pos = b; vtx_write[1].uv = uv_b; vtx_write[1].col = col; 
+    vtx_write[2].pos = c; vtx_write[2].uv = uv_c; vtx_write[2].col = col; 
+    vtx_write[3].pos = d; vtx_write[3].uv = uv_d; vtx_write[3].col = col;
+    vtx_write += 4;
+    vtx_current_idx += 4;
+    idx_write += 6;
 }
 
 void ImDrawList::PrimQuad(const ImVec2& a, const ImVec2& b, const ImVec2& c, const ImVec2& d, ImU32 col)
 {
     const ImVec2 uv = GImGui->FontTexUvWhitePixel;
-    vtx_write[0].pos = a; vtx_write[0].uv = uv; vtx_write[0].col = col;
-    vtx_write[1].pos = b; vtx_write[1].uv = uv; vtx_write[1].col = col;
-    vtx_write[2].pos = c; vtx_write[2].uv = uv; vtx_write[2].col = col;
-    vtx_write[3].pos = a; vtx_write[3].uv = uv; vtx_write[3].col = col;
-    vtx_write[4].pos = c; vtx_write[4].uv = uv; vtx_write[4].col = col;
-    vtx_write[5].pos = d; vtx_write[5].uv = uv; vtx_write[5].col = col;
-    vtx_write += 6;
+    idx_write[0] = vtx_current_idx; idx_write[1] = vtx_current_idx+1; idx_write[2] = vtx_current_idx+2; 
+    idx_write[3] = vtx_current_idx; idx_write[4] = vtx_current_idx+2; idx_write[5] = vtx_current_idx+3; 
+    vtx_write[0].pos = a; vtx_write[0].uv = uv; vtx_write[0].col = col; 
+    vtx_write[1].pos = b; vtx_write[1].uv = uv; vtx_write[1].col = col; 
+    vtx_write[2].pos = c; vtx_write[2].uv = uv; vtx_write[2].col = col; 
+    vtx_write[3].pos = d; vtx_write[3].uv = uv; vtx_write[3].col = col; 
+    vtx_write += 4;
+    vtx_current_idx += 4;
+    idx_write += 6;
 }
 
 // FIXME-OPT: In many instances the caller could provide a normal.
@@ -7774,7 +7794,7 @@ void ImDrawList::AddLine(const ImVec2& a, const ImVec2& b, ImU32 col, float thic
     if ((col >> 24) == 0)
         return;
 
-    PrimReserve(6);
+    PrimReserve(6, 4);
     PrimLine(a, b, col, thickness);
 }
 
@@ -7796,27 +7816,31 @@ void ImDrawList::AddArcFast(const ImVec2& center, float radius, ImU32 col, int a
         }
         circle_vtx_builds = true;
     }
-    
-    const ImVec2 uv = GImGui->FontTexUvWhitePixel;
+
     if (filled)
     {
-        PrimReserve((unsigned int)(a_max-a_min) * 3);
-        for (int a0 = a_min; a0 < a_max; a0++)
+        PrimReserve((unsigned int)(a_max-a_min) * 3, (unsigned int)(a_max-a_min+1) + 1);
+        ImDrawIdx idx = vtx_current_idx;
+        for (int a = 0; a < a_max - a_min; a++)
         {
-            int a1 = (a0 + 1 == SAMPLES) ? 0 : a0 + 1;
-            PrimVtx(center + circle_vtx[a0] * radius, uv, col);
-            PrimVtx(center + circle_vtx[a1] * radius, uv, col);
-            PrimVtx(center + third_point_offset, uv, col);
+            PrimIdx(idx + 1 + a);
+            PrimIdx(idx + 1 + a + 1);
+            PrimIdx(idx);
         }
+        const ImVec2 uv = GImGui->FontTexUvWhitePixel;
+        PrimVtx(center + third_point_offset, uv, col);
+        for (int a = a_min; a < a_max+1; a++)
+            PrimVtx(center + circle_vtx[(a >= SAMPLES) ? a - SAMPLES : a] * radius, uv, col);
     }
     else
     {
-        PrimReserve((unsigned int)(a_max-a_min) * 6);
+        // FIXME-OPT: Wasting vertices.
+        PrimReserve((unsigned int)(a_max-a_min) * 6, (unsigned int)(a_max-a_min) * 4);
         for (int a0 = a_min; a0 < a_max; a0++)
-        {
+		{
             int a1 = (a0 + 1 == SAMPLES) ? 0 : a0 + 1;
             PrimLine(center + circle_vtx[a0] * radius, center + circle_vtx[a1] * radius, col);
-        }
+		}
     }
 }
 
@@ -7831,7 +7855,7 @@ void ImDrawList::AddRect(const ImVec2& a, const ImVec2& b, ImU32 col, float roun
 
     if (r == 0.0f || rounding_corners == 0)
     {
-        PrimReserve(4*6);
+        PrimReserve(6*4, 4*4);
         PrimLine(ImVec2(a.x,a.y), ImVec2(b.x,a.y), col);
         PrimLine(ImVec2(b.x,a.y), ImVec2(b.x,b.y), col);
         PrimLine(ImVec2(b.x,b.y), ImVec2(a.x,b.y), col);
@@ -7839,7 +7863,7 @@ void ImDrawList::AddRect(const ImVec2& a, const ImVec2& b, ImU32 col, float roun
     }
     else
     {
-        PrimReserve(4*6);
+        PrimReserve(6*4, 4*4);
         PrimLine(ImVec2(a.x + ((rounding_corners & 1)?r:0), a.y), ImVec2(b.x - ((rounding_corners & 2)?r:0), a.y), col);
         PrimLine(ImVec2(b.x, a.y + ((rounding_corners & 2)?r:0)), ImVec2(b.x, b.y - ((rounding_corners & 4)?r:0)), col);
         PrimLine(ImVec2(b.x - ((rounding_corners & 4)?r:0), b.y), ImVec2(a.x + ((rounding_corners & 8)?r:0), b.y), col);
@@ -7861,16 +7885,15 @@ void ImDrawList::AddRectFilled(const ImVec2& a, const ImVec2& b, ImU32 col, floa
     r = ImMin(r, fabsf(b.x-a.x) * ( ((rounding_corners&(1|2))==(1|2)) || ((rounding_corners&(4|8))==(4|8)) ? 0.5f : 1.0f ));
     r = ImMin(r, fabsf(b.y-a.y) * ( ((rounding_corners&(1|8))==(1|8)) || ((rounding_corners&(2|4))==(2|4)) ? 0.5f : 1.0f ));
 
-    const ImVec2 uv = GImGui->FontTexUvWhitePixel;
     if (r == 0.0f || rounding_corners == 0)
     {
         // Use triangle so we can merge more draw calls together (at the cost of extra vertices)
-        PrimReserve(6);
+        PrimReserve(6, 4);
         PrimRect(a, b, col);
     }
     else
     {
-        PrimReserve(6+6*2);
+        PrimReserve(6*3, 4*3);
         PrimRect(ImVec2(a.x+r,a.y), ImVec2(b.x-r,b.y), col);
         
         float top_y = (rounding_corners & 1) ? a.y+r : a.y;
@@ -7893,7 +7916,7 @@ void ImDrawList::AddTriangleFilled(const ImVec2& a, const ImVec2& b, const ImVec
     if ((col >> 24) == 0)
         return;
 
-    PrimReserve(3);
+    PrimReserve(3, 3);
     PrimTriangle(a, b, c, col);
 }
 
@@ -7902,14 +7925,18 @@ void ImDrawList::AddCircle(const ImVec2& centre, float radius, ImU32 col, int nu
     if ((col >> 24) == 0)
         return;
 
-    PrimReserve((unsigned int)num_segments*6);
+    PrimReserve(num_segments * 6, num_segments * 4);
+
     const float a_step = 2*PI/(float)num_segments;
     float a0 = 0.0f;
+    ImVec2 p0 = centre + ImVec2(cosf(a0), sinf(a0)) * radius;
     for (int i = 0; i < num_segments; i++)
     {
         const float a1 = (i + 1) == num_segments ? 0.0f : a0 + a_step;
-        PrimLine(centre + ImVec2(cosf(a0), sinf(a0))*radius, centre + ImVec2(cosf(a1), sinf(a1))*radius, col);
+        const ImVec2 p1 = centre + ImVec2(cosf(a1), sinf(a1)) * radius;
+        PrimLine(p0, p1, col);
         a0 = a1;
+        p0 = p1;
     }
 }
 
@@ -7919,16 +7946,18 @@ void ImDrawList::AddCircleFilled(const ImVec2& centre, float radius, ImU32 col,
         return;
 
     const ImVec2 uv = GImGui->FontTexUvWhitePixel;
-    PrimReserve((unsigned int)num_segments*3);
+    const ImDrawIdx idx = vtx_current_idx;
+    PrimReserve((unsigned int)(num_segments*3), (unsigned int)(1 + num_segments));
+
     const float a_step = 2*PI/(float)num_segments;
     float a0 = 0.0f;
-    for (int i = 0; i < num_segments; i++)
+    PrimVtx(centre, uv, col);
+    for (int i = 0; i < num_segments; i++, a0 += a_step)
     {
-        const float a1 = (i + 1) == num_segments ? 0.0f : a0 + a_step;
-        PrimVtx(centre + ImVec2(cosf(a0), sinf(a0))*radius, uv, col);
-        PrimVtx(centre + ImVec2(cosf(a1), sinf(a1))*radius, uv, col);
-        PrimVtx(centre, uv, col);
-        a0 = a1;
+        PrimVtx(centre + ImVec2(cosf(a0), sinf(a0)) * radius, uv, col);
+        PrimIdx(idx);
+        PrimIdx(idx + 1 + i);
+        PrimIdx(idx + 1 + ((i + 1 == num_segments) ? 0 : i + 1));
     }
 }
 
@@ -7946,17 +7975,24 @@ void ImDrawList::AddText(const ImFont* font, float font_size, const ImVec2& pos,
 
     // reserve vertices for worse case
     const unsigned int char_count = (unsigned int)(text_end - text_begin);
-    const unsigned int vtx_count_max = char_count * 6;
+    const unsigned int vtx_count_max = char_count * 4;
+    const unsigned int idx_count_max = char_count * 6;
     const size_t vtx_begin = vtx_buffer.size();
-    PrimReserve(vtx_count_max);
+    const size_t idx_begin = idx_buffer.size();
+    PrimReserve(idx_count_max, vtx_count_max);
 
     font->RenderText(font_size, pos, col, clip_rect_stack.back(), text_begin, text_end, this, wrap_width, cpu_clip_max);
 
     // give back unused vertices
+    // FIXME-OPT
     vtx_buffer.resize((size_t)(vtx_write - &vtx_buffer.front()));
-    const size_t vtx_count = vtx_buffer.size() - vtx_begin;
-    commands.back().vtx_count -= (unsigned int)(vtx_count_max - vtx_count);
-    vtx_write -= (vtx_count_max - vtx_count);
+    idx_buffer.resize((size_t)(idx_write - &idx_buffer.front()));
+    unsigned int vtx_unused = vtx_count_max - (unsigned int)(vtx_buffer.size() - vtx_begin);
+    unsigned int idx_unused = idx_count_max - (unsigned int)(idx_buffer.size() - idx_begin);
+    commands.back().idx_count -= idx_unused;
+    vtx_write -= vtx_unused;
+    idx_write -= idx_unused;
+    vtx_current_idx = (ImDrawIdx)vtx_buffer.size();
 }
 
 void ImDrawList::AddImage(ImTextureID user_texture_id, const ImVec2& a, const ImVec2& b, const ImVec2& uv0, const ImVec2& uv1, ImU32 col)
@@ -7969,7 +8005,7 @@ void ImDrawList::AddImage(ImTextureID user_texture_id, const ImVec2& a, const Im
     if (push_texture_id)
         PushTextureID(user_texture_id);
 
-    PrimReserve(6);
+    PrimReserve(6, 4);
     PrimRectUV(a, b, uv0, uv1, col);
 
     if (push_texture_id)
@@ -9010,7 +9046,9 @@ void ImFont::RenderText(float size, ImVec2 pos, ImU32 col, const ImVec4& clip_re
     float x = pos.x;
     float y = pos.y;
 
-    ImDrawVert* out_vertices = draw_list->vtx_write;
+    ImDrawVert* vtx_write = draw_list->vtx_write;
+    ImDrawIdx vtx_current_idx = draw_list->vtx_current_idx;
+    ImDrawIdx* idx_write = draw_list->idx_write;
 
     const char* s = text_begin;
     while (s < text_end)
@@ -9100,26 +9138,18 @@ void ImFont::RenderText(float size, ImVec2 pos, ImU32 col, const ImVec4& clip_re
                         }
 
                         // NB: we are not calling PrimRectUV() here because non-inlined causes too much overhead in a debug build.
-                        out_vertices[0].pos = ImVec2(x1, y1);
-                        out_vertices[0].uv  = ImVec2(u1, v1);
-                        out_vertices[0].col = col;
-
-                        out_vertices[1].pos = ImVec2(x2, y1);
-                        out_vertices[1].uv  = ImVec2(u2, v1);
-                        out_vertices[1].col = col;
-
-                        out_vertices[2].pos = ImVec2(x2, y2);
-                        out_vertices[2].uv  = ImVec2(u2, v2);
-                        out_vertices[2].col = col;
-
-                        out_vertices[3] = out_vertices[0];
-                        out_vertices[4] = out_vertices[2];
-
-                        out_vertices[5].pos = ImVec2(x1, y2);
-                        out_vertices[5].uv  = ImVec2(u1, v2);
-                        out_vertices[5].col = col;
-
-                        out_vertices += 6;
+                        // inlined:
+                        {
+                            idx_write[0] = vtx_current_idx; idx_write[1] = vtx_current_idx+1; idx_write[2] = vtx_current_idx+2; 
+                            idx_write[3] = vtx_current_idx; idx_write[4] = vtx_current_idx+2; idx_write[5] = vtx_current_idx+3; 
+                            vtx_write[0].pos.x = x1; vtx_write[0].pos.y = y1; vtx_write[0].col = col; vtx_write[0].uv.x = u1; vtx_write[0].uv.y = v1;
+                            vtx_write[1].pos.x = x2; vtx_write[1].pos.y = y1; vtx_write[1].col = col; vtx_write[1].uv.x = u2; vtx_write[1].uv.y = v1;
+                            vtx_write[2].pos.x = x2; vtx_write[2].pos.y = y2; vtx_write[2].col = col; vtx_write[2].uv.x = u2; vtx_write[2].uv.y = v2;
+                            vtx_write[3].pos.x = x1; vtx_write[3].pos.y = y2; vtx_write[3].col = col; vtx_write[3].uv.x = u1; vtx_write[3].uv.y = v2;
+                            vtx_write += 4;
+                            vtx_current_idx += 4;
+                            idx_write += 6;
+                        }
                     }
                 }
             }
@@ -9128,7 +9158,9 @@ void ImFont::RenderText(float size, ImVec2 pos, ImU32 col, const ImVec4& clip_re
         x += char_width;
     }
 
-    draw_list->vtx_write = out_vertices;
+    draw_list->vtx_write = vtx_write;
+    draw_list->vtx_current_idx = vtx_current_idx;
+    draw_list->idx_write = idx_write;
 }
 
 //-----------------------------------------------------------------------------
@@ -10410,14 +10442,14 @@ void ImGui::ShowMetricsWindow(bool* opened)
     {
         ImGui::Text("ImGui %s", ImGui::GetVersion());
         ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", 1000.0f / ImGui::GetIO().Framerate, ImGui::GetIO().Framerate);
-        ImGui::Text("%d vertices", ImGui::GetIO().MetricsRenderVertices);
+        ImGui::Text("%d vertices, %d triangles", ImGui::GetIO().MetricsRenderVertices, ImGui::GetIO().MetricsRenderIndices / 3);
         ImGui::Separator();
 
         struct Funcs
         {
             static void NodeDrawList(ImDrawList* draw_list, const char* label)
             {
-                bool opened = ImGui::TreeNode(draw_list, "%s: %d vtx, %d cmds", label, draw_list->vtx_buffer.size(), draw_list->commands.size());
+                bool opened = ImGui::TreeNode(draw_list, "%s: %d vtx, %d indices, %d cmds", label, draw_list->vtx_buffer.size(), draw_list->idx_buffer.size(), draw_list->commands.size());
                 if (draw_list == ImGui::GetWindowDrawList())
                 {
                     ImGui::SameLine();
@@ -10429,7 +10461,7 @@ void ImGui::ShowMetricsWindow(bool* opened)
                     if (pcmd->user_callback)
                         ImGui::BulletText("Callback %p, user_data %p", pcmd->user_callback, pcmd->user_callback_data);
                     else
-                        ImGui::BulletText("Draw %d vtx, tex = %p", pcmd->vtx_count, pcmd->texture_id);
+                        ImGui::BulletText("Draw %d indexed vtx, tex = %p", pcmd->idx_count, pcmd->texture_id);
                 ImGui::TreePop();
             }
 

imgui.h

@@ -671,6 +671,7 @@ struct ImGuiIO
     bool        WantCaptureKeyboard;        // Widget is active (= ImGui will use your keyboard input)
     float       Framerate;                  // Framerate estimation, in frame per second. Rolling average estimation based on IO.DeltaTime over 120 frames
     int         MetricsRenderVertices;      // Vertices processed during last call to Render()
+    int         MetricsRenderIndices;       // 
 
     //------------------------------------------------------------------
     // [Internal] ImGui will maintain those fields for you
@@ -857,13 +858,16 @@ typedef void (*ImDrawCallback)(const ImDrawList* parent_list, const ImDrawCmd* c
 // Typically, 1 command = 1 gpu draw call (unless command is a callback)
 struct ImDrawCmd
 {
-    unsigned int    vtx_count;                  // Number of vertices (multiple of 3) to be drawn as triangles. The vertices are stored in the callee ImDrawList's vtx_buffer[] array.
+    unsigned int    idx_count;                  // Number of indices (multiple of 3) to be rendered as triangles. Vertices are stored in the callee ImDrawList's vtx_buffer[] array, indices in idx_buffer[].
     ImVec4          clip_rect;                  // Clipping rectangle (x1, y1, x2, y2)
     ImTextureID     texture_id;                 // User-provided texture ID. Set by user in ImfontAtlas::SetTexID() for fonts or passed to Image*() functions. Ignore if never using images or multiple fonts atlas.
     ImDrawCallback  user_callback;              // If != NULL, call the function instead of rendering the vertices. vtx_count will be 0. clip_rect and texture_id will be set normally.
     void*           user_callback_data;         // The draw callback code can access this.
 };
 
+// Vertex index
+typedef unsigned short ImDrawIdx;
+
 // Vertex layout
 #ifndef IMGUI_OVERRIDE_DRAWVERT_STRUCT_LAYOUT
 struct ImDrawVert
@@ -891,11 +895,14 @@ struct ImDrawList
     // This is what you have to render
     ImVector<ImDrawCmd>     commands;           // Commands. Typically 1 command = 1 gpu draw call.
     ImVector<ImDrawVert>    vtx_buffer;         // Vertex buffer. Each command consume ImDrawCmd::vtx_count of those
+    ImVector<ImDrawIdx>     idx_buffer;         // Index buffer. Each command consume ImDrawCmd::idx_count of those
 
     // [Internal to ImGui]
     ImVector<ImVec4>        clip_rect_stack;    // [Internal]
     ImVector<ImTextureID>   texture_id_stack;   // [Internal] 
     ImDrawVert*             vtx_write;          // [Internal] point within vtx_buffer after each add command (to avoid using the ImVector<> operators too much)
+    ImDrawIdx               vtx_current_idx;    // [Internal] == vtx_buffer.size()
+    ImDrawIdx*              idx_write;          // [Internal] point within idx_buffer after each add command (to avoid using the ImVector<> operators too much)
 
     ImDrawList() { Clear(); }
     IMGUI_API void  Clear();
@@ -918,11 +925,11 @@ struct ImDrawList
     IMGUI_API void  AddImage(ImTextureID user_texture_id, const ImVec2& a, const ImVec2& b, const ImVec2& uv0, const ImVec2& uv1, ImU32 col = 0xFFFFFFFF);
 
     // Advanced
-    IMGUI_API void  AddCallback(ImDrawCallback callback, void* callback_data);  // Your rendering function must check for 'user_callback' in ImDrawCmd and call the function instead of rendering triangles.
-    IMGUI_API void  AddDrawCmd();                                               // This is useful if you need to forcefully create a new draw call (to allow for dependent rendering / blending). Otherwise primitives are merged into the same draw-call as much as possible
+    IMGUI_API void  AddCallback(ImDrawCallback callback, void* callback_data);   // Your rendering function must check for 'user_callback' in ImDrawCmd and call the function instead of rendering triangles.
+    IMGUI_API void  AddDrawCmd();               // This is useful if you need to forcefully create a new draw call (to allow for dependent rendering / blending). Otherwise primitives are merged into the same draw-call as much as possible
 
     // Internal helpers
-    IMGUI_API void  PrimReserve(unsigned int vtx_count);
+    IMGUI_API void  PrimReserve(unsigned int idx_count, unsigned int vtx_count);
     IMGUI_API void  PrimTriangle(const ImVec2& a, const ImVec2& b, const ImVec2& c, ImU32 col);
     IMGUI_API void  PrimRect(const ImVec2& a, const ImVec2& b, ImU32 col);
     IMGUI_API void  PrimRectUV(const ImVec2& a, const ImVec2& b, const ImVec2& uv_a, const ImVec2& uv_b, ImU32 col);
@@ -930,7 +937,8 @@ struct ImDrawList
     IMGUI_API void  PrimLine(const ImVec2& a, const ImVec2& b, ImU32 col, float thickness = 1.0f);
     IMGUI_API void  UpdateClipRect();
     IMGUI_API void  UpdateTextureID();
-    IMGUI_API void  PrimVtx(const ImVec2& pos, const ImVec2& uv, ImU32 col)  { vtx_write->pos = pos; vtx_write->uv = uv; vtx_write->col = col; vtx_write++; }
+    IMGUI_API void  PrimVtx(const ImVec2& pos, const ImVec2& uv, ImU32 col)   { vtx_write->pos = pos; vtx_write->uv = uv; vtx_write->col = col; vtx_write++; vtx_current_idx++; }
+    IMGUI_API void  PrimIdx(unsigned int idx)                                 { *idx_write++ = (ImDrawIdx)idx; }
 };
 
 // Load and rasterize multiple TTF fonts into a same texture.