til_fb: introduce a fragment texture source

Idea here is to provide texture sources for obtaining pixel
colors at the til_fb_put_pixel/fill drawing API, making it
possible for at least overlayable modules to serve as
mask/stencil operators where their drawn areas are populated by
the contents of another fragment produced dynamically,
potentially by other modules altogether.

This commit adds a texture=modulename option to the compose
module for specifying if a texture should be used when
compositing, excepting and defaulting to "none" for disabling
texturing.

A future commit should expand this compose option to accept a
potential list of modules for composing the texture in the same
way as the main layers= list functions.

Something this all immediately makes clear is the need for
a better settings syntax, probably in the form of all module
setting specifiers optionally being followed by a squence
of settings, with support for escaping to handle nested
situations.

1 files changed, 9 insertions, 7 deletions

diff --git a/src/sdl_fb.c b/src/sdl_fb.c
index 249d746..b260091 100644
--- a/src/sdl_fb.c
+++ b/src/sdl_fb.c
@@ -202,13 +202,15 @@ static void * sdl_fb_page_alloc(til_fb_t *fb, void *context, til_fb_page_t *res_
 	/* 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.pitch = p->surface->pitch >> 2;
-	res_page->fragment.stride = res_page->fragment.pitch - c->width;
+	*res_page =	(til_fb_page_t){
+				.fragment.buf = p->surface->pixels,
+				.fragment.width = c->width,
+				.fragment.frame_width = c->width,
+				.fragment.height = c->height,
+				.fragment.frame_height = c->height,
+				.fragment.pitch = p->surface->pitch >> 2,
+				.fragment.stride = (p->surface->pitch >> 2) - c->width,
+			};
 
 	return p;
 }