Examples: OpenGL3: Create the VAO in the render function so the setup can more easily be used with multiple shared GL context. (#1217)

examples/opengl3_example/imgui_impl_glfw_gl3.cpp

@@ -13,6 +13,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2018-02-23: OpenGL: Create the VAO in the render function so the setup can more easily be used with multiple shared GL context.
 //  2018-02-20: Inputs: Added support for mouse cursors (ImGui::GetMouseCursor() value and WM_SETCURSOR message handling).
 //  2018-02-20: Inputs: Renamed GLFW callbacks exposed in .h to not include GL3 in their name.
 //  2018-02-16: Misc: Obsoleted the io.RenderDrawListsFn callback and exposed ImGui_ImplGlfwGL3_RenderDrawData() in the .h file so you can call it yourself.
@@ -54,7 +55,7 @@ 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 unsigned int g_VboHandle = 0, g_VaoHandle = 0, g_ElementsHandle = 0;
+static unsigned int g_VboHandle = 0, g_ElementsHandle = 0;
 
 // OpenGL3 Render function.
 // (this used to be set in io.RenderDrawListsFn and called by ImGui::Render(), but you can now call this directly from your main loop)
@@ -113,9 +114,22 @@ void ImGui_ImplGlfwGL3_RenderDrawData(ImDrawData* draw_data)
     glUseProgram(g_ShaderHandle);
     glUniform1i(g_AttribLocationTex, 0);
     glUniformMatrix4fv(g_AttribLocationProjMtx, 1, GL_FALSE, &ortho_projection[0][0]);
-    glBindVertexArray(g_VaoHandle);
     glBindSampler(0, 0); // Rely on combined texture/sampler state.
 
+    // 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);
+    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));
+
+    // Draw
     for (int n = 0; n < draw_data->CmdListsCount; n++)
     {
         const ImDrawList* cmd_list = draw_data->CmdLists[n];
@@ -289,17 +303,6 @@ bool ImGui_ImplGlfwGL3_CreateDeviceObjects()
     glGenBuffers(1, &g_VboHandle);
     glGenBuffers(1, &g_ElementsHandle);
 
-    glGenVertexArrays(1, &g_VaoHandle);
-    glBindVertexArray(g_VaoHandle);
-    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));
-
     ImGui_ImplGlfwGL3_CreateFontsTexture();
 
     // Restore modified GL state
@@ -312,10 +315,9 @@ bool ImGui_ImplGlfwGL3_CreateDeviceObjects()
 
 void    ImGui_ImplGlfwGL3_InvalidateDeviceObjects()
 {
-    if (g_VaoHandle) glDeleteVertexArrays(1, &g_VaoHandle);
     if (g_VboHandle) glDeleteBuffers(1, &g_VboHandle);
     if (g_ElementsHandle) glDeleteBuffers(1, &g_ElementsHandle);
-    g_VaoHandle = g_VboHandle = g_ElementsHandle = 0;
+    g_VboHandle = g_ElementsHandle = 0;
 
     if (g_ShaderHandle && g_VertHandle) glDetachShader(g_ShaderHandle, g_VertHandle);
     if (g_VertHandle) glDeleteShader(g_VertHandle);

examples/sdl_opengl3_example/imgui_impl_sdl_gl3.cpp

@@ -12,6 +12,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2018-02-23: OpenGL: Create the VAO in the render function so the setup can more easily be used with multiple shared GL context.
 //  2018-02-16: Inputs: Added support for mouse cursors, honoring ImGui::GetMouseCursor() value.
 //  2018-02-16: Misc: Obsoleted the io.RenderDrawListsFn callback and exposed ImGui_ImplSdlGL3_RenderDrawData() in the .h file so you can call it yourself.
 //  2018-02-06: Misc: Removed call to ImGui::Shutdown() which is not available from 1.60 WIP, user needs to call CreateContext/DestroyContext themselves.
@@ -38,15 +39,17 @@
 #include <SDL_syswm.h>
 #include <GL/gl3w.h>    // This example is using gl3w to access OpenGL functions (because it is small). You may use glew/glad/glLoadGen/etc. whatever already works for you.
 
-// Data
+// SDL data
 static Uint64       g_Time = 0;
 static bool         g_MousePressed[3] = { false, false, false };
+static SDL_Cursor*  g_MouseCursors[ImGuiMouseCursor_Count_] = { 0 };
+
+// OpenGL data
 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 unsigned int g_VboHandle = 0, g_VaoHandle = 0, g_ElementsHandle = 0;
-static SDL_Cursor*  g_MouseCursors[ImGuiMouseCursor_Count_] = { 0 };
+static unsigned int g_VboHandle = 0,g_ElementsHandle = 0;
 
 // This is the main rendering function that you have to implement and provide to ImGui (via setting up 'RenderDrawListsFn' in the ImGuiIO structure)
 // Note that this implementation is little overcomplicated because we are saving/setting up/restoring every OpenGL state explicitly, in order to be able to run within any OpenGL engine that doesn't do so. 
@@ -105,9 +108,22 @@ void ImGui_ImplSdlGL3_RenderDrawData(ImDrawData* draw_data)
     glUseProgram(g_ShaderHandle);
     glUniform1i(g_AttribLocationTex, 0);
     glUniformMatrix4fv(g_AttribLocationProjMtx, 1, GL_FALSE, &ortho_projection[0][0]);
-    glBindVertexArray(g_VaoHandle);
     glBindSampler(0, 0); // Rely on combined texture/sampler state.
 
+    // 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);
+    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));
+
+    // Draw
     for (int n = 0; n < draw_data->CmdListsCount; n++)
     {
         const ImDrawList* cmd_list = draw_data->CmdLists[n];
@@ -289,17 +305,6 @@ bool ImGui_ImplSdlGL3_CreateDeviceObjects()
     glGenBuffers(1, &g_VboHandle);
     glGenBuffers(1, &g_ElementsHandle);
 
-    glGenVertexArrays(1, &g_VaoHandle);
-    glBindVertexArray(g_VaoHandle);
-    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));
-
     ImGui_ImplSdlGL3_CreateFontsTexture();
 
     // Restore modified GL state
@@ -312,10 +317,9 @@ bool ImGui_ImplSdlGL3_CreateDeviceObjects()
 
 void    ImGui_ImplSdlGL3_InvalidateDeviceObjects()
 {
-    if (g_VaoHandle) glDeleteVertexArrays(1, &g_VaoHandle);
     if (g_VboHandle) glDeleteBuffers(1, &g_VboHandle);
     if (g_ElementsHandle) glDeleteBuffers(1, &g_ElementsHandle);
-    g_VaoHandle = g_VboHandle = g_ElementsHandle = 0;
+    g_VboHandle = g_ElementsHandle = 0;
 
     if (g_ShaderHandle && g_VertHandle) glDetachShader(g_ShaderHandle, g_VertHandle);
     if (g_VertHandle) glDeleteShader(g_VertHandle);