Demo: Comments (#1408)

imgui.h

@@ -129,7 +129,7 @@ namespace ImGui
 
     // Demo/Debug/Info
     IMGUI_API void          ShowTestWindow(bool* p_open = NULL);        // create demo/test window. demonstrate most ImGui features. call this to learn about the library! try to make it always available in your application!
-    IMGUI_API void          ShowMetricsWindow(bool* p_open = NULL);     // create metrics window. display ImGui internals: browse window list, draw commands, individual vertices, basic internal state, etc.
+    IMGUI_API void          ShowMetricsWindow(bool* p_open = NULL);     // create metrics window. display ImGui internals: draw commands (with individual draw calls and vertices), window list, basic internal state, etc.
     IMGUI_API void          ShowStyleEditor(ImGuiStyle* ref = NULL);    // add style editor block (not a window). you can pass in a reference ImGuiStyle structure to compare to, revert to and save to (else it uses the default style)
     IMGUI_API void          ShowUserGuide();                            // add basic help/info block (not a window): how to manipulate ImGui as a end-user (mouse/keyboard controls).
 

imgui_demo.cpp

@@ -543,17 +543,27 @@ void ImGui::ShowTestWindow(bool* p_open)
         {
             ImGui::TextWrapped("Below we are displaying the font texture (which is the only texture we have access to in this demo). Use the 'ImTextureID' type as storage to pass pointers or identifier to your own texture data. Hover the texture for a zoomed view!");
             ImVec2 tex_screen_pos = ImGui::GetCursorScreenPos();
-            float tex_w = (float)ImGui::GetIO().Fonts->TexWidth;
-            float tex_h = (float)ImGui::GetIO().Fonts->TexHeight;
-            ImTextureID tex_id = ImGui::GetIO().Fonts->TexID;
+            ImGuiIO& io = ImGui::GetIO();
+
+            // Here we are grabbing the font texture because that's the only one we have access to inside the demo code.
+            // Remember that ImTextureID is just storage for whatever you want it to be, it is essentially a value that will be passed to the render function inside the ImDrawCmd structure.
+            // If you use one of the default imgui_impl_XXXX.cpp renderer, they all have comments at the top of their file to specify what they expect to be stored in ImTextureID.
+            // (for example, the imgui_impl_dx11.cpp renderer expect a 'ID3D11ShaderResourceView*' pointer. The imgui_impl_glfw_gl3.cpp renderer expect a GLuint OpenGL texture identifier etc.)
+            // If you decided that ImTextureID = MyEngineTexture*, then you can pass your MyEngineTexture* pointers to ImGui::Image(), and gather width/height through your own functions, etc.
+            // Using ShowMetricsWindow() as a "debugger" to inspect the draw data that are being passed to your render will help you debug issues if you are confused about this.
+            // Consider using the lower-level ImDrawList::AddImage() API, via ImGui::GetWindowDrawList()->AddImage().
+            ImTextureID tex_id = io.Fonts->TexID; 
+            float tex_w = (float)io.Fonts->TexWidth;
+            float tex_h = (float)io.Fonts->TexHeight;
+
             ImGui::Text("%.0fx%.0f", tex_w, tex_h);
             ImGui::Image(tex_id, ImVec2(tex_w, tex_h), ImVec2(0,0), ImVec2(1,1), ImColor(255,255,255,255), ImColor(255,255,255,128));
             if (ImGui::IsItemHovered())
             {
                 ImGui::BeginTooltip();
                 float focus_sz = 32.0f;
-                float focus_x = ImGui::GetMousePos().x - tex_screen_pos.x - focus_sz * 0.5f; if (focus_x < 0.0f) focus_x = 0.0f; else if (focus_x > tex_w - focus_sz) focus_x = tex_w - focus_sz;
-                float focus_y = ImGui::GetMousePos().y - tex_screen_pos.y - focus_sz * 0.5f; if (focus_y < 0.0f) focus_y = 0.0f; else if (focus_y > tex_h - focus_sz) focus_y = tex_h - focus_sz;
+                float focus_x = io.MousePos.x - tex_screen_pos.x - focus_sz * 0.5f; if (focus_x < 0.0f) focus_x = 0.0f; else if (focus_x > tex_w - focus_sz) focus_x = tex_w - focus_sz;
+                float focus_y = io.MousePos.y - tex_screen_pos.y - focus_sz * 0.5f; if (focus_y < 0.0f) focus_y = 0.0f; else if (focus_y > tex_h - focus_sz) focus_y = tex_h - focus_sz;
                 ImGui::Text("Min: (%.2f, %.2f)", focus_x, focus_y);
                 ImGui::Text("Max: (%.2f, %.2f)", focus_x + focus_sz, focus_y + focus_sz);
                 ImVec2 uv0 = ImVec2((focus_x) / tex_w, (focus_y) / tex_h);