SDL3窗口缩放时正方形变形问题及解决方案咨询

我尝试使用SDL3及SDL_SetRenderLogicalPresentation()函数，搭配SDL_LOGICAL_PRESENTATION_LETTERBOX模式，实现窗口缩放时保持正方形的尺寸与比例，编写的Python代码如下：

import sdl3

# Function to draw a square
def draw_square(renderer, x, y, size):
    sdl3.SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255)  # White color
    rect = sdl3.SDL_FRect(x=x, y=y, w=size, h=size)
    sdl3.SDL_RenderFillRect(renderer, rect)

# Initialize SDL3
if sdl3.SDL_Init(sdl3.SDL_INIT_VIDEO) < 0:
    print(f"SDL initialization error: {sdl3.SDL_GetError().decode()}")
    exit(1)

# Create window
window = sdl3.SDL_CreateWindow(b"Hello World", 640, 480, sdl3.SDL_WINDOW_RESIZABLE)
if not window:
    print(f"Window creation error: {sdl3.SDL_GetError().decode()}")
    exit(1)

# Create renderer
renderer = sdl3.SDL_CreateRenderer(window, b"metal")
if not renderer:
    print(f"Renderer creation error: {sdl3.SDL_GetError().decode()}")
    exit(1)

# Set logical rendering size
logical_width, logical_height = 640, 480
sdl3.SDL_SetRenderLogicalPresentation(renderer, logical_width, logical_height, sdl3.SDL_LOGICAL_PRESENTATION_LETTERBOX)

# Parameters for positioning the square
square_size = 100  # Fixed square size
square_x = (logical_width - square_size) / 2  # Center horizontally
square_y = (logical_height - square_size) / 2  # Center vertically

running = True
while running:
    # Event handling
    event = sdl3.SDL_Event()
    while sdl3.SDL_PollEvent(event):
        if event.type == sdl3.SDL_EVENT_QUIT:
            running = False

    # Rendering
    sdl3.SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255)  # Black background
    sdl3.SDL_RenderClear(renderer)
    # Draw square with fixed size and centered position
    draw_square(renderer, square_x, square_y, square_size)
    sdl3.SDL_RenderPresent(renderer)

# Cleanup
sdl3.SDL_DestroyRenderer(renderer)
sdl3.SDL_DestroyWindow(window)
sdl3.SDL_Quit()

目前，正方形仅在释放鼠标（缩放结束）后才会恢复原有宽高，而在缩放过程中会被拉伸或挤压出现变形。

请问：

1. 这是SDL_SetRenderLogicalPresentation的预期行为吗？
2. 如何实现窗口缩放全程无变形的正方形？是否有可行的解决方法或最佳实践（我是Mac用户）？
3. 将正方形转换为纹理是否有助于稳定其比例？

解答 #

1. 这是预期行为吗？ #

是的，这种现象在SDL3搭配macOS Metal渲染器的场景下属于预期行为。默认情况下，SDL不会在窗口拖动缩放的每一步自动更新逻辑渲染的映射关系，仅在缩放操作完成（鼠标释放）时才重新计算适配规则，目的是避免频繁更新带来的性能开销。

2. 实现全程无变形的解决方法 #

核心思路是监听窗口尺寸变化事件，实时更新逻辑渲染设置。具体操作：

• 在事件循环中监听SDL_EVENT_WINDOW_SIZE_CHANGED事件（该事件会在窗口尺寸发生任何变化时触发，包括拖动缩放的过程中）
• 每次触发事件时，重新调用SDL_SetRenderLogicalPresentation，强制SDL更新逻辑坐标到窗口坐标的映射

修改后的Python代码示例：

import sdl3

# Function to draw a square
def draw_square(renderer, x, y, size):
    sdl3.SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255)  # White color
    rect = sdl3.SDL_FRect(x=x, y=y, w=size, h=size)
    sdl3.SDL_RenderFillRect(renderer, rect)

# Initialize SDL3
if sdl3.SDL_Init(sdl3.SDL_INIT_VIDEO) < 0:
    print(f"SDL initialization error: {sdl3.SDL_GetError().decode()}")
    exit(1)

# Create window
window = sdl3.SDL_CreateWindow(b"Hello World", 640, 480, sdl3.SDL_WINDOW_RESIZABLE)
if not window:
    print(f"Window creation error: {sdl3.SDL_GetError().decode()}")
    exit(1)

# Create renderer
renderer = sdl3.SDL_CreateRenderer(window, b"metal")
if not renderer:
    print(f"Renderer creation error: {sdl3.SDL_GetError().decode()}")
    exit(1)

# Set logical rendering size
logical_width, logical_height = 640, 480
sdl3.SDL_SetRenderLogicalPresentation(renderer, logical_width, logical_height, sdl3.SDL_LOGICAL_PRESENTATION_LETTERBOX)

# Parameters for positioning the square
square_size = 100  # Fixed square size
square_x = (logical_width - square_size) / 2  # Center horizontally
square_y = (logical_height - square_size) / 2  # Center vertically

running = True
while running:
    # Event handling
    event = sdl3.SDL_Event()
    while sdl3.SDL_PollEvent(event):
        if event.type == sdl3.SDL_EVENT_QUIT:
            running = False
        # 监听窗口尺寸变化事件，实时更新逻辑渲染设置
        elif event.type == sdl3.SDL_EVENT_WINDOW_SIZE_CHANGED:
            sdl3.SDL_SetRenderLogicalPresentation(renderer, logical_width, logical_height, sdl3.SDL_LOGICAL_PRESENTATION_LETTERBOX)

    # Rendering
    sdl3.SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255)  # Black background
    sdl3.SDL_RenderClear(renderer)
    # Draw square with fixed size and centered position
    draw_square(renderer, square_x, square_y, square_size)
    sdl3.SDL_RenderPresent(renderer)

# Cleanup
sdl3.SDL_DestroyRenderer(renderer)
sdl3.SDL_DestroyWindow(window)
sdl3.SDL_Quit()

3. 转换为纹理是否有用？ #

作用不大。问题的根源是逻辑渲染的映射关系没有实时更新，而非绘制方式的问题。即使将正方形转为纹理，它依然会受到逻辑坐标到窗口坐标映射的影响，缩放过程中同样会出现变形。因此，核心解决方案还是实时更新逻辑渲染设置。

内容的提问来源于stack exchange，提问作者werwer werwer