c++ - SDL_RenderSetScale 和 SDL_RenderDrawLine 如何交互？

Question

根据 SDL2 wiki 上 SDL_RenderSetScale() 和 SDL_RenderSetLogicalSize() 的简短描述，我的印象是这些命令独立于其内容缩放整个帧，基本上与您在图形编辑器中缩放图像的方式相同。

在我以前的程序中，我只缩放和渲染 SDL_Rects 和 SDL_Textures，情况似乎是这样。然而，使用 RenderDrawLine() 绘制线条只是部分情况。

如果直线平行于 x 轴或 y 轴，则它会正确缩放，但在任何其他情况下，它根本不会缩放。

SDL_RenderSetScale( gRenderer, gScaler, gScaler ); 
SDL_SetRenderDrawColor( gRenderer, 0x00, 0x00, 0x00, 0xFF );
SDL_RenderClear( gRenderer );
SDL_SetRenderDrawColor( gRenderer, 0xFF, 0xFF, 0xFF, 0xFF );
SDL_RenderDrawLine( gRenderer, x1, y1, x2, y2 );
SDL_RenderPresent( gRenderer );

有没有办法使用 SDL_RenderSetScale() 来缩放线条而不考虑角度？该函数如何决定缩放什么和忽略什么？

Answer 1

这是SDL渲染器的一个已知bug，画线功能不能缩放然后以自由角度绘制。它仍然存在于最近发布的 SDL-2.0.6 中(参见 /* FIXME: We can't use a rect for this line... */ ):

static int
RenderDrawLinesWithRects(SDL_Renderer * renderer,
                     const SDL_Point * points, int count)
{
    SDL_FRect *frect;
    SDL_FRect *frects;
    SDL_FPoint fpoints[2];
    int i, nrects;
    int status;

    frects = SDL_stack_alloc(SDL_FRect, count-1);
    if (!frects) {
        return SDL_OutOfMemory();
    }

    status = 0;
    nrects = 0;
    for (i = 0; i < count-1; ++i) {
        if (points[i].x == points[i+1].x) {
            int minY = SDL_min(points[i].y, points[i+1].y);
            int maxY = SDL_max(points[i].y, points[i+1].y);

            frect = &frects[nrects++];
            frect->x = points[i].x * renderer->scale.x;
            frect->y = minY * renderer->scale.y;
            frect->w = renderer->scale.x;
            frect->h = (maxY - minY + 1) * renderer->scale.y;
        } else if (points[i].y == points[i+1].y) {
            int minX = SDL_min(points[i].x, points[i+1].x);
            int maxX = SDL_max(points[i].x, points[i+1].x);

            frect = &frects[nrects++];
            frect->x = minX * renderer->scale.x;
            frect->y = points[i].y * renderer->scale.y;
            frect->w = (maxX - minX + 1) * renderer->scale.x;
            frect->h = renderer->scale.y;
        } else {
            /* FIXME: We can't use a rect for this line... */
            fpoints[0].x = points[i].x * renderer->scale.x;
            fpoints[0].y = points[i].y * renderer->scale.y;
            fpoints[1].x = points[i+1].x * renderer->scale.x;
            fpoints[1].y = points[i+1].y * renderer->scale.y;
            status += renderer->RenderDrawLines(renderer, fpoints, 2);
        }
    }

    status += renderer->RenderFillRects(renderer, frects, nrects);

    SDL_stack_free(frects);

    if (status < 0) {
        status = -1;
    }
    return status;
}

我认为这不会很快得到解决，因为这是一个很少使用的功能。