Examples: OpenGL2/3: save/restore some more state correctly.

Might save an hour of staring at blank-screen to 5% of the population,
worth it.

examples/README.txt

@@ -2,7 +2,7 @@ Those are standalone ready-to-build applications to demonstrate ImGui.
 Binaries of some of those demos are available at http://www.miracleworld.net/imgui/binaries
   
 TL;DR; 
- Refer to 'opengl_example' (not 'opengl3_example') to understand how the library is setup.
+ Refer to 'opengl_example' to understand how the library is setup, because it is the simplest one.
  Copy the imgui_impl_xxx.cpp/.h files you need if you are using one of provided rendering/IO backends.
  If using different or your own backend, copy opengl_example/imgui_impl_opengl.cpp/.h to get started.
  
@@ -25,13 +25,12 @@ opengl_example/
     OpenGL example, using GLFW + fixed pipeline.
     This is simple and should work for all OpenGL enabled applications.
     Prefer following this example to learn how ImGui works!
+	(You can use this code in a GL3/GL4 context but make sure you disable the programmable pipeline
+	by calling "glUseProgram(0)" before ImGui::Render.)
 
 opengl3_example/
     OpenGL example, using GLFW/GL3W + programmable pipeline.
-    This uses more modern OpenGL calls and custom shaders.
-    Even if your application is using modern OpenGL you are better off copying the code from the fixed
-    pipeline version! I don't think there is an advantage using this over the simpler example, but it is 
-    provided for reference.
+    This uses more modern OpenGL calls and custom shaders. It's more messy.
 
 directx9_example/
     DirectX9 example, Windows only.

examples/opengl3_example/imgui_impl_glfw_gl3.cpp

@@ -30,10 +30,15 @@ static unsigned int g_VboHandle = 0, g_VaoHandle = 0, g_ElementsHandle = 0;
 // - in your Render function, try translating your projection matrix by (0.5f,0.5f) or (0.375f,0.375f)
 static void ImGui_ImplGlfwGL3_RenderDrawLists(ImDrawData* draw_data)
 {
-    // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled
-    GLint last_program, last_texture;
+    // Backup GL state
+    GLint last_program, last_texture, last_array_buffer, last_element_array_buffer, last_vertex_array;
     glGetIntegerv(GL_CURRENT_PROGRAM, &last_program);
     glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
+    glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &last_array_buffer);
+    glGetIntegerv(GL_ELEMENT_ARRAY_BUFFER_BINDING, &last_element_array_buffer);
+    glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array);
+
+    // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled
     glEnable(GL_BLEND);
     glBlendEquation(GL_FUNC_ADD);
     glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
@@ -87,13 +92,13 @@ static void ImGui_ImplGlfwGL3_RenderDrawLists(ImDrawData* draw_data)
         }
     }
 
-    // Restore modified state
-    glBindVertexArray(0);
-    glBindBuffer(GL_ARRAY_BUFFER, 0);
-    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
+    // Restore modified GL state
     glUseProgram(last_program);
-    glDisable(GL_SCISSOR_TEST);
     glBindTexture(GL_TEXTURE_2D, last_texture);
+    glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
+    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, last_element_array_buffer);
+    glBindVertexArray(last_vertex_array);
+    glDisable(GL_SCISSOR_TEST);
 }
 
 static const char* ImGui_ImplGlfwGL3_GetClipboardText()
@@ -162,6 +167,12 @@ void ImGui_ImplGlfwGL3_CreateFontsTexture()
 
 bool ImGui_ImplGlfwGL3_CreateDeviceObjects()
 {
+    // Backup GL state
+    GLint last_texture, last_array_buffer, last_vertex_array;
+    glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
+    glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &last_array_buffer);
+    glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array);
+
     const GLchar *vertex_shader =
         "#version 330\n"
         "uniform mat4 ProjMtx;\n"
@@ -220,11 +231,14 @@ bool ImGui_ImplGlfwGL3_CreateDeviceObjects()
     glVertexAttribPointer(g_AttribLocationUV, 2, GL_FLOAT, GL_FALSE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, uv));
     glVertexAttribPointer(g_AttribLocationColor, 4, GL_UNSIGNED_BYTE, GL_TRUE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, col));
 #undef OFFSETOF
-    glBindVertexArray(0);
-    glBindBuffer(GL_ARRAY_BUFFER, 0);
 
     ImGui_ImplGlfwGL3_CreateFontsTexture();
 
+    // Restore modified GL state
+    glBindTexture(GL_TEXTURE_2D, last_texture);
+    glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
+    glBindVertexArray(last_vertex_array);
+
     return true;
 }
 

examples/opengl_example/imgui_impl_glfw.cpp

@@ -28,6 +28,8 @@ static void ImGui_ImplGlfw_RenderDrawLists(ImDrawData* draw_data)
     // We are using the OpenGL fixed pipeline to make the example code simpler to read!
     // A probable faster way to render would be to collate all vertices from all cmd_lists into a single vertex buffer.
     // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled, vertex/texcoord/color pointers.
+    GLint last_texture;
+    glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
     glPushAttrib(GL_ENABLE_BIT | GL_COLOR_BUFFER_BIT | GL_TRANSFORM_BIT);
     glEnable(GL_BLEND);
     glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
@@ -87,7 +89,7 @@ static void ImGui_ImplGlfw_RenderDrawLists(ImDrawData* draw_data)
     glDisableClientState(GL_COLOR_ARRAY);
     glDisableClientState(GL_TEXTURE_COORD_ARRAY);
     glDisableClientState(GL_VERTEX_ARRAY);
-    glBindTexture(GL_TEXTURE_2D, 0);
+    glBindTexture(GL_TEXTURE_2D, last_texture);
     glMatrixMode(GL_MODELVIEW);
     glPopMatrix();
     glMatrixMode(GL_PROJECTION);
@@ -147,6 +149,8 @@ bool ImGui_ImplGlfw_CreateDeviceObjects()
     io.Fonts->GetTexDataAsAlpha8(&pixels, &width, &height);
 
     // Create texture
+    GLint last_texture;
+    glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
     glGenTextures(1, &g_FontTexture);
     glBindTexture(GL_TEXTURE_2D, g_FontTexture);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
@@ -159,6 +163,7 @@ bool ImGui_ImplGlfw_CreateDeviceObjects()
     // Cleanup (don't clear the input data if you want to append new fonts later)
     io.Fonts->ClearInputData();
     io.Fonts->ClearTexData();
+    glBindTexture(GL_TEXTURE_2D, last_texture);
 
     return true;
 }