Examples: Allegro 5: Added support for 32-bit indices setup via defining ImDrawIdx, to avoid an unecessary conversion (Allegro 5 doesn't support 16-bit indices).

CHANGELOG.txt

@@ -52,6 +52,7 @@ Other Changes:
 - Window: Fixed popups/tooltips/menus not honoring style.DisplaySafeAreaPadding as well as it should have (part of menus displayed outside the safe area, etc.).
 - MenuBar: Made BeginMainMenuBar() honor style.DisplaySafeAreaPadding so the text can be made visible on TV settings that don't display all pixels. (#1439) [@dougbinks]
 - Style: Changed default style.DisplaySafeAreaPadding values from (4,4) to (3,3) so it is smaller than FramePadding and has no effect on main menu bar on a computer. (#1439)
+- Examples: Allegro5: Added support for 32-bit indices setup via defining ImDrawIdx, to avoid an unecessary conversion (Allegro 5 doesn't support 16-bit indices).
 
 -----------------------------------------------------------------------
 

examples/allegro5_example/README.md

@@ -1,15 +1,24 @@
 
+# Configuration
+
+Dear ImGui outputs 16-bit vertex indices by default. 
+Allegro doesn't support them natively, so we have two solutions: convert the indices manually in imgui_impl_a5.cpp, or compile imgui with 32-bit indices.
+You can either modify imconfig.h that comes with Dear ImGui (easier), or set a C++ preprocessor option IMGUI_USER_CONFIG to find to a filename.
+We are providing `imconfig_allegro5.h` that enables 32-bit indices.
+Note that the back-end supports _BOTH_ 16-bit and 32-bit indices, but 32-bit indices will be slightly faster as they won't require a manual conversion.
+
 # How to Build
 
 - On Ubuntu 14.04+
 
 ```bash
-g++ -I ../.. main.cpp imgui_impl_a5.cpp ../../imgui*.cpp -lallegro -lallegro_primitives -o allegro5_example
+g++ -DIMGUI_USER_CONFIG=\"examples/allegro5_example/imconfig_allegro5.h\" -I ../.. main.cpp imgui_impl_a5.cpp ../../imgui*.cpp -lallegro -lallegro_primitives -o allegro5_example
 ```
 
 - On Windows with Visual Studio's CLI
 
 ```
 set ALLEGRODIR=path_to_your_allegro5_folder
-cl /Zi /MD /I %ALLEGRODIR%\include /I ..\.. main.cpp imgui_impl_a5.cpp ..\..\imgui*.cpp /link /LIBPATH:%ALLEGRODIR%\lib allegro-5.0.10-monolith-md.lib user32.lib
+set IMCONFIG_FILE=\"examples/allegro5_example/imconfig_allegro5.h\"
+cl /Zi /MD /I %ALLEGRODIR%\include /DIMGUI_USER_CONFIG=%IMCONFIG_FILE% /I ..\.. main.cpp imgui_impl_a5.cpp ..\..\imgui*.cpp /link /LIBPATH:%ALLEGRODIR%\lib allegro-5.0.10-monolith-md.lib user32.lib
 ```

examples/allegro5_example/imconfig_allegro5.h

@@ -0,0 +1,11 @@
+//-----------------------------------------------------------------------------
+// COMPILE-TIME OPTIONS FOR DEAR IMGUI ALLEGRO 5 EXAMPLE
+// See imconfig.h for the full template
+// Because Allegro doesn't support 16-bit vertex indices, we enable the compile-time option of imgui to use 32-bit indices
+//-----------------------------------------------------------------------------
+
+#pragma once
+
+// Use 32-bit vertex indices because Allegro doesn't support 16-bit ones
+// This allows us to avoid converting vertices format at runtime
+#define ImDrawIdx  int

examples/allegro5_example/imgui_impl_a5.cpp

@@ -12,6 +12,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2018-04-18: Misc: Added support for 32-bits vertex indices to avoid conversion at runtime. Added imconfig_allegro5.h to enforce 32-bit indices when included from imgui.h.
 //  2018-02-16: Misc: Obsoleted the io.RenderDrawListsFn callback and exposed ImGui_ImplA5_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.
 //  2018-02-06: Inputs: Added mapping for ImGuiKey_Space.
@@ -67,12 +68,21 @@ void ImGui_ImplA5_RenderDrawData(ImDrawData* draw_data)
             vertices[i] = v;
         }
 
-        // FIXME-OPT: Unfortunately Allegro doesn't support 16-bit indices
-        // You can also use '#define ImDrawIdx unsigned int' in imconfig.h and request ImGui to output 32-bit indices
-        static ImVector<int> indices;
-        indices.resize(cmd_list->IdxBuffer.Size);
+        const int* indices = NULL;
+        if (sizeof(ImDrawIdx) == 2)
+        {
+            // FIXME-OPT: Unfortunately Allegro doesn't support 16-bit indices.. You can '#define ImDrawIdx  int' in imconfig.h to request ImGui to output 32-bit indices.
+            // Otherwise, we convert them from 16-bit to 32-bit at runtime here, which works perfectly but is a little wasteful.
+            static ImVector<int> indices_converted;
+            indices_converted.resize(cmd_list->IdxBuffer.Size);
             for (int i = 0; i < cmd_list->IdxBuffer.Size; ++i)
-            indices[i] = (int)cmd_list->IdxBuffer.Data[i];
+                indices_converted[i] = (int)cmd_list->IdxBuffer.Data[i];
+            indices = indices_converted.Data;
+        }
+        else if (sizeof(ImDrawIdx) == 4)
+        {
+            indices = (const int*)cmd_list->IdxBuffer.Data;
+        }
 
         int idx_offset = 0;
         for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)