(Breaking) Moved ImDrawCallback_ResetRenderState -> ImGui::GetPlatformIO().DrawCallback_ResetRenderState + added room in ImGuiPlatformIO for more standard backend-agnostic draw callbacks. (#9378)

imgui.h

@@ -3166,12 +3166,6 @@ typedef unsigned short ImDrawIdx;   // Default: 16-bit (for maximum compatibilit
 typedef void (*ImDrawCallback)(const ImDrawList* parent_list, const ImDrawCmd* cmd);
 #endif
 
-// Special Draw callback value to request renderer backend to reset the graphics/render state.
-// The renderer backend needs to handle this special value, otherwise it will crash trying to call a function at this address.
-// This is useful, for example, if you submitted callbacks which you know have altered the render state and you want it to be restored.
-// Render state is not reset by default because they are many perfectly useful way of altering render state (e.g. changing shader/blending settings before an Image call).
-#define ImDrawCallback_ResetRenderState     (ImDrawCallback)(-8)
-
 // Typically, 1 command = 1 GPU draw call (unless command is a callback)
 // - VtxOffset: When 'io.BackendFlags & ImGuiBackendFlags_RendererHasVtxOffset' is enabled,
 //   this fields allow us to render meshes larger than 64K vertices while keeping 16-bit indices.
@@ -3378,7 +3372,8 @@ struct ImDrawList
 
     // Advanced: Draw Callbacks
     // - May be used to alter render state (change sampler, blending, current shader). May be used to emit custom rendering commands (difficult to do correctly, but possible).
-    // - Use special ImDrawCallback_ResetRenderState callback to instruct backend to reset its render state to the default.
+    // - Use special GetPlatformIO().DrawCallback_ResetRenderState callback to instruct backend to reset its render state to the default.
+    // - See other standard callbacks in GetPlatformIO(), which may or not be supported by your backend.
     // - Your rendering loop must check for 'UserCallback' in ImDrawCmd and call the function instead of rendering triangles. All standard backends are honoring this.
     // - For some backends, the callback may access selected render-states exposed by the backend in a ImGui_ImplXXXX_RenderState structure pointed to by platform_io.Renderer_RenderState.
     // - IMPORTANT: please be mindful of the different level of indirection between using size==0 (copying argument) and using size>0 (copying pointed data into a buffer).
@@ -4022,6 +4017,12 @@ struct ImGuiPlatformIO
     // Written by some backends during ImGui_ImplXXXX_RenderDrawData() call to point backend_specific ImGui_ImplXXXX_RenderState* structure.
     void*       Renderer_RenderState;
 
+    // Standard draw callbacks
+    ImDrawCallback  DrawCallback_ResetRenderState;      // Request to reset the graphics/render state.
+    ImDrawCallback  DrawCallback_SetSamplerLinear;      // Request to set current texture sampling to Linear
+    ImDrawCallback  DrawCallback_SetSamplerNearest;     // Request to set current texture sampling to Nearest/Point
+    ImDrawCallback  DrawCallback_SetSamplerCustom;      // Request to set current texture sampling using Backend Specific data.
+
     //------------------------------------------------------------------
     // Output
     //------------------------------------------------------------------
@@ -4150,6 +4151,8 @@ namespace ImGui
     //static inline void  SetScrollPosHere()                    { SetScrollHere(); }                                                // OBSOLETED in 1.42
 }
 
+#define ImDrawCallback_ResetRenderState     (ImDrawCallback)(-8)    // OBSOLETED in 1.92.8: Use ImGui::GetPlatformIO().DrawCallback_ResetRenderState
+
 //-- OBSOLETED in 1.92.0: ImFontAtlasCustomRect becomes ImTextureRect
 // - ImFontAtlasCustomRect::X,Y          --> ImTextureRect::x,y
 // - ImFontAtlasCustomRect::Width,Height --> ImTextureRect::w,h