Backends: Allegro5: Fixed mishandling of the ImDrawCmd::IdxOffset field. (#4790)

backends/imgui_impl_allegro5.cpp

@@ -16,6 +16,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2021-12-08: Renderer: Fixed mishandling of the the ImDrawCmd::IdxOffset field! This is an old bug but it never had an effect until some internal rendering changes in 1.86.
 //  2021-08-17: Calling io.AddFocusEvent() on ALLEGRO_EVENT_DISPLAY_SWITCH_OUT/ALLEGRO_EVENT_DISPLAY_SWITCH_IN events.
 //  2021-06-29: Reorganized backend to pull data from a single structure to facilitate usage with multiple-contexts (all g_XXXX access changed to bd->XXXX).
 //  2021-05-19: Renderer: Replaced direct access to ImDrawCmd::TextureId with a call to ImDrawCmd::GetTexID(). (will become a requirement)
@@ -155,7 +156,6 @@ void ImGui_ImplAllegro5_RenderDrawData(ImDrawData* draw_data)
         }
 
         // Render command lists
-        int idx_offset = 0;
         ImVec2 clip_off = draw_data->DisplayPos;
         for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)
         {
@@ -180,9 +180,8 @@ void ImGui_ImplAllegro5_RenderDrawData(ImDrawData* draw_data)
                 // Apply scissor/clipping rectangle, Draw
                 ALLEGRO_BITMAP* texture = (ALLEGRO_BITMAP*)pcmd->GetTexID();
                 al_set_clipping_rectangle(clip_min.x, clip_min.y, clip_max.x - clip_min.x, clip_max.y - clip_min.y);
-                al_draw_prim(&vertices[0], bd->VertexDecl, texture, idx_offset, idx_offset + pcmd->ElemCount, ALLEGRO_PRIM_TRIANGLE_LIST);
+                al_draw_prim(&vertices[0], bd->VertexDecl, texture, pcmd->IdxOffset, pcmd->IdxOffset + pcmd->ElemCount, ALLEGRO_PRIM_TRIANGLE_LIST);
             }
-            idx_offset += pcmd->ElemCount;
         }
     }
 

docs/CHANGELOG.txt

@@ -90,8 +90,8 @@ Other Changes:
 - Backends: Vulkan: Call vkCmdSetScissor() at the end of render with a full-viewport to reduce
   likehood of issues with people using VK_DYNAMIC_STATE_SCISSOR in their app without calling
   vkCmdSetScissor() explicitly every frame. (#4644)
-- Backends: OpenGL2, Marmalade: Fixed mishandling of the ImDrawCmd::IdxOffset field. This is an old bug,
-  but due to the way we created drawlists, it never had any visible side-effect before.
+- Backends: OpenGL2, Allegro5, Marmalade: Fixed mishandling of the ImDrawCmd::IdxOffset field.
+  This is an old bug, but due to the way we created drawlists, it never had any visible side-effect before.
   The new code for handling Modal and CTRL+Tab dimming/whitening recently made the bug surface. (#4790)
 - Backends: DX12: Fixed DRAW_EMPTY_SCISSOR_RECTANGLE warnings. (#4775)
 - Backends: SDL_Renderer: Added support for large meshes (64k+ vertices) with 16-bit indices,