til_fb: til_fb_fragment_t.{pitch,stride} uint32_t units

Originally it seemed sensible to make these units of bytes, for
flexibility reasons.

But it's advantageous for everything to be able to assume pixels
are always 4-byte/32-bit aligned.  Having the stride/pitch be in
bytes of units made it theoretically possible to produce
unaligned rows of pixels, which would break that assumption.

I don't think anything was ever actually producing such things,
and I've added some asserts to the {sdl,drm}_fb.c page
acquisition code to go fatal on such pages.

This change required going through all the modules and get rid of
their uint32_t vs. void* dances and other such 1-byte vs. 4-byte
scaling arithmetic.

Code is simpler now, and probably faster in some cases.  And now
allows future work to just assume things cna always occur 4-bytes
at a time without concern for unaligned accesses.

1 files changed, 5 insertions, 2 deletions

diff --git a/src/sdl_fb.c b/src/sdl_fb.c
index 2605d6c..249d746 100644
--- a/src/sdl_fb.c
+++ b/src/sdl_fb.c
@@ -199,13 +199,16 @@ static void * sdl_fb_page_alloc(til_fb_t *fb, void *context, til_fb_page_t *res_
 
 	p->surface = SDL_CreateRGBSurface(0, c->width, c->height, 32, 0, 0, 0, 0);
 
+	/* rototiller wants to assume all pixels to be 32-bit aligned, so prevent unaligning pitches */
+	assert(!(p->surface->pitch & 0x3));
+
 	res_page->fragment.buf = p->surface->pixels;
 	res_page->fragment.width = c->width;
 	res_page->fragment.frame_width = c->width;
 	res_page->fragment.height = c->height;
 	res_page->fragment.frame_height = c->height;
-	res_page->fragment.stride = p->surface->pitch - (c->width * 4);
-	res_page->fragment.pitch = p->surface->pitch;
+	res_page->fragment.pitch = p->surface->pitch >> 2;
+	res_page->fragment.stride = res_page->fragment.pitch - c->width;
 
 	return p;
 }