renderer: refactor pl_render_target.dst_rect

[jojo61]

Your refactor commit 65e5e17 breaks the scaling form SD (720x576) to HD (1920x1080) in my applikation.
No changes on my side where done.

[jojo61]

Ok I found it. In renderer.c you scaled x and y with the same factor. Thats wrong. Here a fixed excerpt:

// Adjust the src rect corresponding to the rounded crop
float scale = pl_rect_w(*src) / pl_rect_w(*dst),
      base_x = src->x0,
      base_y = src->y0;

float scale_h = pl_rect_h(*src) / pl_rect_h(*dst);


src->x0 = base_x + (rx0 - dst->x0) * scale;
src->x1 = base_x + (rx1 - dst->x0) * scale;
src->y0 = base_y + (ry0 - dst->y0) * scale_h;
src->y1 = base_y + (ry1 - dst->y0) * scale_h;

// Update dst_rect to the rounded values and re-apply flip if needed. We
// always do this in the `dst_rect` rather than the `src_rect` because this
// allows e.g. polar sampling compute shaders to work.
*dst = (struct pl_rect2df) {
    .x0 = flipped_x ? rx1 : rx0,
    .y0 = flipped_y ? ry1 : ry0,
    .x1 = flipped_x ? rx0 : rx1,
    .y1 = flipped_y ? ry0 : ry1,
};