Examples: OpenGL3: Minor tweaks, clarifications + not calling glBindBuffer more than necessary in the render loop.

docs/CHANGELOG.txt

@@ -43,6 +43,7 @@ Other Changes:
 - Inputs: Also add support for horizontal scroll with Shift+Mouse Wheel. (#2424, #1463) [@LucaRood]
 - Examples: OpenGL: Added a dummy GL call + comments in ImGui_ImplOpenGL3_Init() to detect uninitialized
   GL function loaders early, and help users understand what they are missing. (#2421)
+- Examples: OpenGL3: Minor tweaks + not calling glBindBuffer more than necessary in the render loop.
 - Examples: FreeGLUT: Made io.DeltaTime always > 0. (#2430)
 
 

examples/imgui_impl_allegro5.cpp

@@ -154,7 +154,7 @@ bool ImGui_ImplAllegro5_CreateDeviceObjects()
 {
     // Build texture atlas
     ImGuiIO &io = ImGui::GetIO();
-    unsigned char *pixels;
+    unsigned char* pixels;
     int width, height;
     io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height);
 

examples/imgui_impl_opengl3.cpp

@@ -12,6 +12,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2019-03-29: OpenGL: Not calling glBindBuffer more than necessary in the render loop.
 //  2019-03-15: OpenGL: Added a dummy GL call + comments in ImGui_ImplOpenGL3_Init() to detect uninitialized GL function loaders early.
 //  2019-03-03: OpenGL: Fix support for ES 2.0 (WebGL 1.0).
 //  2019-02-20: OpenGL: Fix for OSX not supporting OpenGL 4.5, we don't try to read GL_CLIP_ORIGIN even if defined by the headers/loader.
@@ -104,8 +105,8 @@
 static char         g_GlslVersionString[32] = "";
 static GLuint       g_FontTexture = 0;
 static GLuint       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 int          g_AttribLocationTex = 0, g_AttribLocationProjMtx = 0;                                // Uniforms location
+static int          g_AttribLocationVtxPos = 0, g_AttribLocationVtxUV = 0, g_AttribLocationVtxColor = 0; // Vertex attributes location
 static unsigned int g_VboHandle = 0, g_ElementsHandle = 0;
 
 // Functions
@@ -170,7 +171,7 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
 #endif
     GLint last_array_buffer; glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &last_array_buffer);
 #ifndef IMGUI_IMPL_OPENGL_ES2
-    GLint last_vertex_array; glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array);
+    GLint last_vertex_array_object; glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array_object);
 #endif
 #ifdef GL_POLYGON_MODE
     GLint last_polygon_mode[2]; glGetIntegerv(GL_POLYGON_MODE, last_polygon_mode);
@@ -226,20 +227,23 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
     glBindSampler(0, 0); // We use combined texture/sampler state. Applications using GL 3.3 may set that otherwise.
 #endif
 
+    // Recreate the VAO every time (this is to easily allow multiple GL contexts to be rendered to. VAO are not shared among GL contexts)
+    // The renderer would actually work without any VAO bound, but then our VertexAttrib calls would overwrite the default one currently bound.
 #ifndef IMGUI_IMPL_OPENGL_ES2
-    // Recreate the VAO every time
-    // (This is to easily allow multiple GL contexts. VAO are not shared among GL contexts, and we don't track creation/deletion of windows so we don't have an obvious key to use to cache them.)
-    GLuint vao_handle = 0;
-    glGenVertexArrays(1, &vao_handle);
-    glBindVertexArray(vao_handle);
+    GLuint vertex_array_object = 0;
+    glGenVertexArrays(1, &vertex_array_object);
+    glBindVertexArray(vertex_array_object);
 #endif
+
+    // Bind vertex/index buffers and setup attributes for ImDrawVert
     glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
-    glEnableVertexAttribArray(g_AttribLocationPosition);
-    glEnableVertexAttribArray(g_AttribLocationUV);
-    glEnableVertexAttribArray(g_AttribLocationColor);
-    glVertexAttribPointer(g_AttribLocationPosition, 2, GL_FLOAT, GL_FALSE, sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, pos));
-    glVertexAttribPointer(g_AttribLocationUV, 2, GL_FLOAT, GL_FALSE, sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, uv));
-    glVertexAttribPointer(g_AttribLocationColor, 4, GL_UNSIGNED_BYTE, GL_TRUE, sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, col));
+    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, g_ElementsHandle);
+    glEnableVertexAttribArray(g_AttribLocationVtxPos);
+    glEnableVertexAttribArray(g_AttribLocationVtxUV);
+    glEnableVertexAttribArray(g_AttribLocationVtxColor);
+    glVertexAttribPointer(g_AttribLocationVtxPos,   2, GL_FLOAT,         GL_FALSE, sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, pos));
+    glVertexAttribPointer(g_AttribLocationVtxUV,    2, GL_FLOAT,         GL_FALSE, sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, uv));
+    glVertexAttribPointer(g_AttribLocationVtxColor, 4, GL_UNSIGNED_BYTE, GL_TRUE,  sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, col));
 
     // Will project scissor/clipping rectangles into framebuffer space
     ImVec2 clip_off = draw_data->DisplayPos;         // (0,0) unless using multi-viewports
@@ -251,10 +255,8 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
         const ImDrawList* cmd_list = draw_data->CmdLists[n];
         size_t idx_buffer_offset = 0;
 
-        glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
+        // Upload vertex/index buffers
         glBufferData(GL_ARRAY_BUFFER, (GLsizeiptr)cmd_list->VtxBuffer.Size * sizeof(ImDrawVert), (const GLvoid*)cmd_list->VtxBuffer.Data, GL_STREAM_DRAW);
-
-        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, g_ElementsHandle);
         glBufferData(GL_ELEMENT_ARRAY_BUFFER, (GLsizeiptr)cmd_list->IdxBuffer.Size * sizeof(ImDrawIdx), (const GLvoid*)cmd_list->IdxBuffer.Data, GL_STREAM_DRAW);
 
         for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)
@@ -280,7 +282,7 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
                     if (clip_origin_lower_left)
                         glScissor((int)clip_rect.x, (int)(fb_height - clip_rect.w), (int)(clip_rect.z - clip_rect.x), (int)(clip_rect.w - clip_rect.y));
                     else
-                        glScissor((int)clip_rect.x, (int)clip_rect.y, (int)clip_rect.z, (int)clip_rect.w); // Support for GL 4.5's glClipControl(GL_UPPER_LEFT)
+                        glScissor((int)clip_rect.x, (int)clip_rect.y, (int)clip_rect.z, (int)clip_rect.w); // Support for GL 4.5 rarely used glClipControl(GL_UPPER_LEFT)
 
                     // Bind texture, Draw
                     glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->TextureId);
@@ -290,8 +292,10 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
             idx_buffer_offset += pcmd->ElemCount * sizeof(ImDrawIdx);
         }
     }
+
+    // Destroy the temporary VAO
 #ifndef IMGUI_IMPL_OPENGL_ES2
-    glDeleteVertexArrays(1, &vao_handle);
+    glDeleteVertexArrays(1, &vertex_array_object);
 #endif
 
     // Restore modified GL state
@@ -302,7 +306,7 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
 #endif
     glActiveTexture(last_active_texture);
 #ifndef IMGUI_IMPL_OPENGL_ES2
-    glBindVertexArray(last_vertex_array);
+    glBindVertexArray(last_vertex_array_object);
 #endif
     glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
     glBlendEquationSeparate(last_blend_equation_rgb, last_blend_equation_alpha);
@@ -554,9 +558,9 @@ bool    ImGui_ImplOpenGL3_CreateDeviceObjects()
 
     g_AttribLocationTex = glGetUniformLocation(g_ShaderHandle, "Texture");
     g_AttribLocationProjMtx = glGetUniformLocation(g_ShaderHandle, "ProjMtx");
-    g_AttribLocationPosition = glGetAttribLocation(g_ShaderHandle, "Position");
-    g_AttribLocationUV = glGetAttribLocation(g_ShaderHandle, "UV");
-    g_AttribLocationColor = glGetAttribLocation(g_ShaderHandle, "Color");
+    g_AttribLocationVtxPos = glGetAttribLocation(g_ShaderHandle, "Position");
+    g_AttribLocationVtxUV = glGetAttribLocation(g_ShaderHandle, "UV");
+    g_AttribLocationVtxColor = glGetAttribLocation(g_ShaderHandle, "Color");
 
     // Create buffers
     glGenBuffers(1, &g_VboHandle);

examples/imgui_impl_vulkan.cpp

@@ -221,7 +221,7 @@ void ImGui_ImplVulkan_RenderDrawData(ImDrawData* draw_data, VkCommandBuffer comm
     if (!fd->IndexBuffer || fd->IndexBufferSize < index_size)
         CreateOrResizeBuffer(fd->IndexBuffer, fd->IndexBufferMemory, fd->IndexBufferSize, index_size, VK_BUFFER_USAGE_INDEX_BUFFER_BIT);
 
-    // Upload Vertex and index Data:
+    // Upload vertex/index data into a single contiguous GPU buffer
     {
         ImDrawVert* vtx_dst = NULL;
         ImDrawIdx* idx_dst = NULL;
@@ -305,6 +305,7 @@ void ImGui_ImplVulkan_RenderDrawData(ImDrawData* draw_data, VkCommandBuffer comm
             const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
             if (pcmd->UserCallback)
             {
+                // User callback (registered via ImDrawList::AddCallback)
                 pcmd->UserCallback(cmd_list, pcmd);
             }
             else

imgui.h

@@ -19,7 +19,7 @@ Index of this file:
 // Misc data structures (ImGuiInputTextCallbackData, ImGuiSizeCallbackData, ImGuiPayload)
 // Obsolete functions
 // Helpers (ImGuiOnceUponAFrame, ImGuiTextFilter, ImGuiTextBuffer, ImGuiStorage, ImGuiListClipper, ImColor)
-// Draw List API (ImDrawCmd, ImDrawIdx, ImDrawVert, ImDrawChannel, ImDrawListFlags, ImDrawList, ImDrawData)
+// Draw List API (ImDrawCallback, ImDrawCmd, ImDrawIdx, ImDrawVert, ImDrawChannel, ImDrawListFlags, ImDrawList, ImDrawData)
 // Font API (ImFontConfig, ImFontGlyph, ImFontGlyphRangesBuilder, ImFontAtlasFlags, ImFontAtlas, ImFont)
 
 */