fix: Blending rendering anomaly when using the software renderer with SDL_WINDOW_TRANSPARENT on Windows. (#13866)

2026-04-22 23:35:39 +00:00 · 2025-09-04 22:41:45 +08:00
parent ea1a769322
commit f2d2cd8152
4 changed files with 388 additions and 4 deletions
--- a/test/testsoftwaretransparent.c
+++ b/test/testsoftwaretransparent.c
@@ -0,0 +1,155 @@
+/*
+  Copyright (C) 1997-2025 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely.
+*/
+#include <SDL3/SDL.h>
+#include <SDL3/SDL_main.h>
+
+#include "glass.h"
+
+
+int main(int argc, char *argv[])
+{
+    const char *image_file = NULL;
+    SDL_Window *window = NULL;
+    SDL_Renderer *renderer = NULL;
+    SDL_Texture *texture = NULL;
+    SDL_WindowFlags flags;
+    bool done = false;
+    SDL_Event event;
+    
+    int return_code = 1;
+
+
+    int windowWidth = 800;
+    int windowHeight = 600;
+    SDL_FRect destRect;
+    destRect.x = 0;
+    destRect.y = 0;
+    destRect.w = 100;
+    destRect.h = 100;
+
+    SDL_FRect destRect2;
+    destRect2.x = 700;
+    destRect2.y = 0;
+    destRect2.w = 100;
+    destRect2.h = 100;
+
+    SDL_FRect destRect3;
+    destRect3.x = 0;
+    destRect3.y = 500;
+    destRect3.w = 100;
+    destRect3.h = 100;
+
+    SDL_FRect destRect4;
+    destRect4.x = 700;
+    destRect4.y = 500;
+    destRect4.w = 100;
+    destRect4.h = 100;
+
+    SDL_FRect destRect5;
+    destRect5.x = 350;
+    destRect5.y = 250;
+    destRect5.w = 100;
+    destRect5.h = 100;
+
+
+    /* Create the window hidden */
+    flags = (SDL_WINDOW_HIDDEN |  SDL_WINDOW_TRANSPARENT);
+    //flags |= SDL_WINDOW_BORDERLESS;
+
+    window = SDL_CreateWindow("SDL Software Renderer Transparent Test", windowWidth, windowHeight, flags);
+    if (!window) {
+        SDL_Log("Couldn't create transparent window: %s", SDL_GetError());
+        goto quit;
+    }
+
+    /* Create a software renderer and set the blend mode */
+    renderer = SDL_CreateRenderer(window, SDL_SOFTWARE_RENDERER);
+    if (!renderer) {
+        SDL_Log("Couldn't create renderer: %s", SDL_GetError());
+        goto quit;
+    }
+
+    if (!SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND)) {
+        SDL_Log("Couldn't set renderer blend mode: %s\n", SDL_GetError());
+        return false;
+    }
+
+    /* Create texture and set the blend mode */
+    // texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA32, SDL_TEXTUREACCESS_TARGET, windowWidth, windowHeight);
+    //texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_TARGET, windowWidth, windowHeight);
+    // texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_BGRA32, SDL_TEXTUREACCESS_TARGET, windowWidth, windowHeight);
+    texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_BGRA8888, SDL_TEXTUREACCESS_TARGET, windowWidth, windowHeight);
+    if (texture == NULL) {
+        SDL_Log("Couldn't create texture: %s\n", SDL_GetError());
+        return false;
+    }
+
+    if (!SDL_SetTextureBlendMode(texture, SDL_BLENDMODE_BLEND_PREMULTIPLIED)) {
+        SDL_Log("Couldn't set texture blend mode: %s\n", SDL_GetError());
+        return false;
+    }
+
+    /* Show */
+    SDL_ShowWindow(window);
+
+    /* We're ready to go! */
+    while (!done) {
+        while (SDL_PollEvent(&event)) {
+            switch (event.type) {
+            case SDL_EVENT_KEY_DOWN:
+                if (event.key.key == SDLK_ESCAPE) {
+                    done = true;
+                }
+                break;
+            case SDL_EVENT_QUIT:
+                done = true;
+                break;
+            default:
+                break;
+            }
+        }
+
+        
+        /* Draw opaque red squares at the four corners of the form, and draw a red square with an alpha value of 180 in the center of the form */
+        
+        SDL_SetRenderTarget(renderer, texture);
+        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 0);
+        SDL_RenderClear(renderer);
+
+        SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);
+        SDL_RenderFillRect(renderer, &destRect);
+        SDL_RenderFillRect(renderer, &destRect2);
+        SDL_RenderFillRect(renderer, &destRect3);
+        SDL_RenderFillRect(renderer, &destRect4);
+        SDL_SetRenderDrawColor(renderer, 255, 0, 0, 180);
+        SDL_RenderFillRect(renderer, &destRect5);
+
+        SDL_SetRenderTarget(renderer, NULL);
+        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 0);
+        SDL_RenderClear(renderer);
+        SDL_RenderTexture(renderer, texture, NULL, NULL);
+
+        /* Show everything on the screen and wait a bit */
+        SDL_RenderPresent(renderer);
+        SDL_Delay(100);
+    }
+
+    /* Success! */
+    return_code = 0;
+
+quit:
+    SDL_DestroyTexture(texture);
+    SDL_DestroyRenderer(renderer);
+    SDL_DestroyWindow(window);
+    SDL_Quit();
+    return return_code;
+}