[SDL] Bad math in SDL_RenderCopy
authorSam Lantinga <slouken@libsdl.org>
Sat, 03 Oct 2009 16:23:16 +0000
changeset 3333b334b4f7dfa0
parent 3332 da1cb54d74ef
child 3334 61ea9005fddf
[SDL] Bad math in SDL_RenderCopy

Mason Wheeler to sdl

When I tried to render an image using something other than NULL for srcrect, it got horribly distorted. I traced it down to the fact that the math in the rectangle adjustments performed just before the call to renderer->RenderCopy is written inside out. It should look like this:

if (dstrect->w != real_dstrect.w) {
int deltax = (dstrect->x - real_dstrect.x);
int deltaw = (dstrect->w - real_dstrect.w);
real_srcrect.x += (deltax * real_srcrect.w) / dstrect->w;
real_srcrect.w += (deltaw * real_srcrect.w) / dstrect->w;
}
if (dstrect->h != real_dstrect.h) {
int deltay = (dstrect->y - real_dstrect.y);
int deltah = (dstrect->h - real_dstrect.h);
real_srcrect.y += (deltay * real_srcrect.h) / dstrect->h;
real_srcrect.h += (deltah * real_srcrect.h) / dstrect->h;
src/video/SDL_video.c
     1.1 --- a/src/video/SDL_video.c	Fri Oct 02 13:50:36 2009 +0000
     1.2 +++ b/src/video/SDL_video.c	Sat Oct 03 16:23:16 2009 +0000
     1.3 @@ -2463,14 +2463,14 @@
     1.4          if (dstrect->w != real_dstrect.w) {
     1.5              int deltax = (real_dstrect.x - dstrect->x);
     1.6              int deltaw = (real_dstrect.w - dstrect->w);
     1.7 -            real_srcrect.x += (deltax * dstrect->w) / real_srcrect.w;
     1.8 -            real_srcrect.w += (deltaw * dstrect->w) / real_srcrect.w;
     1.9 +            real_srcrect.x += (deltax * real_srcrect.w) / dstrect->w;
    1.10 +            real_srcrect.w += (deltaw * real_srcrect.w) / dstrect->w;
    1.11          }
    1.12          if (dstrect->h != real_dstrect.h) {
    1.13              int deltay = (real_dstrect.y - dstrect->y);
    1.14              int deltah = (real_dstrect.h - dstrect->h);
    1.15 -            real_srcrect.y += (deltay * dstrect->h) / real_srcrect.h;
    1.16 -            real_srcrect.h += (deltah * dstrect->h) / real_srcrect.h;
    1.17 +            real_srcrect.y += (deltay * real_srcrect.h) / dstrect->h;
    1.18 +            real_srcrect.h += (deltah * real_srcrect.h) / dstrect->h;
    1.19          }
    1.20      }
    1.21