Backends: OpenGL2, OpenGL3: set GL_UNPACK_ALIGNMENT to 1 before updating textures. (#8802)

backends/imgui_impl_opengl2.cpp

@@ -25,6 +25,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2025-07-15: OpenGL: Set GL_UNPACK_ALIGNMENT to 1 before updating textures. (#8802)
 //  2025-06-11: OpenGL: Added support for ImGuiBackendFlags_RendererHasTextures, for dynamic font atlas. Removed ImGui_ImplOpenGL2_CreateFontsTexture() and ImGui_ImplOpenGL2_DestroyFontsTexture().
 //  2024-10-07: OpenGL: Changed default texture sampler to Clamp instead of Repeat/Wrap.
 //  2024-06-28: OpenGL: ImGui_ImplOpenGL2_NewFrame() recreates font texture if it has been destroyed by ImGui_ImplOpenGL2_DestroyFontsTexture(). (#7748)
@@ -285,6 +286,7 @@ void ImGui_ImplOpenGL2_UpdateTexture(ImTextureData* tex)
         GL_CALL(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP));
         GL_CALL(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP));
         GL_CALL(glPixelStorei(GL_UNPACK_ROW_LENGTH, 0));
+        GL_CALL(glPixelStorei(GL_UNPACK_ALIGNMENT, 1));
         GL_CALL(glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, tex->Width, tex->Height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels));
 
         // Store identifiers
@@ -304,6 +306,7 @@ void ImGui_ImplOpenGL2_UpdateTexture(ImTextureData* tex)
         GLuint gl_tex_id = (GLuint)(intptr_t)tex->TexID;
         GL_CALL(glBindTexture(GL_TEXTURE_2D, gl_tex_id));
         GL_CALL(glPixelStorei(GL_UNPACK_ROW_LENGTH, tex->Width));
+        GL_CALL(glPixelStorei(GL_UNPACK_ALIGNMENT, 1));
         for (ImTextureRect& r : tex->Updates)
             GL_CALL(glTexSubImage2D(GL_TEXTURE_2D, 0, r.x, r.y, r.w, r.h, GL_RGBA, GL_UNSIGNED_BYTE, tex->GetPixelsAt(r.x, r.y)));
         GL_CALL(glPixelStorei(GL_UNPACK_ROW_LENGTH, 0));

backends/imgui_impl_opengl3.cpp

@@ -23,6 +23,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2025-07-15: OpenGL: Set GL_UNPACK_ALIGNMENT to 1 before updating textures. (#8802)
 //  2025-06-11: OpenGL: Added support for ImGuiBackendFlags_RendererHasTextures, for dynamic font atlas. Removed ImGui_ImplOpenGL3_CreateFontsTexture() and ImGui_ImplOpenGL3_DestroyFontsTexture().
 //  2025-06-04: OpenGL: Made GLES 3.20 contexts not access GL_CONTEXT_PROFILE_MASK nor GL_PRIMITIVE_RESTART. (#8664)
 //  2025-02-18: OpenGL: Lazily reinitialize embedded GL loader for when calling backend from e.g. other DLL boundaries. (#8406)
@@ -709,6 +710,17 @@ static void ImGui_ImplOpenGL3_DestroyTexture(ImTextureData* tex)
 
 void ImGui_ImplOpenGL3_UpdateTexture(ImTextureData* tex)
 {
+    // FIXME: Consider backing up and restoring
+    if (tex->Status == ImTextureStatus_WantCreate || tex->Status == ImTextureStatus_WantUpdates)
+    {
+#ifdef GL_UNPACK_ROW_LENGTH // Not on WebGL/ES
+        GL_CALL(glPixelStorei(GL_UNPACK_ROW_LENGTH, 0));
+#endif
+#ifdef GL_UNPACK_ALIGNMENT
+        GL_CALL(glPixelStorei(GL_UNPACK_ALIGNMENT, 1));
+#endif
+    }
+
     if (tex->Status == ImTextureStatus_WantCreate)
     {
         // Create and upload new texture to graphics system
@@ -728,9 +740,6 @@ void ImGui_ImplOpenGL3_UpdateTexture(ImTextureData* tex)
         GL_CALL(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR));
         GL_CALL(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE));
         GL_CALL(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE));
-#ifdef GL_UNPACK_ROW_LENGTH // Not on WebGL/ES
-        GL_CALL(glPixelStorei(GL_UNPACK_ROW_LENGTH, 0));
-#endif
         GL_CALL(glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, tex->Width, tex->Height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels));
 
         // Store identifiers

backends/imgui_impl_opengl3_loader.h

@@ -166,6 +166,7 @@ typedef khronos_uint8_t GLubyte;
 #define GL_SCISSOR_BOX                    0x0C10
 #define GL_SCISSOR_TEST                   0x0C11
 #define GL_UNPACK_ROW_LENGTH              0x0CF2
+#define GL_UNPACK_ALIGNMENT               0x0CF5
 #define GL_PACK_ALIGNMENT                 0x0D05
 #define GL_MAX_TEXTURE_SIZE               0x0D33
 #define GL_TEXTURE_2D                     0x0DE1

docs/CHANGELOG.txt

@@ -45,6 +45,8 @@ Other Changes:
 
 - Error Handling: minor improvements to error handling for TableGetSortSpecs()
   and TableSetBgColor() calls. (#1651, #8499)
+- Backends: OpenGL2, OpenGL3: set GL_UNPACK_ALIGNMENT to 1 before updating 
+  textures. (#8802) [@Daandelange]
 
 
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