[PATCH weston] gl-renderer: compress pixman bands to simplify geometry

[Pekka Paalanen]

On Thu, 16 Oct 2014 16:37:02 -0500
Derek Foreman <derekf at osg.samsung.com> wrote:

> Pixman uses y-x banded rectangles to represent regions.  We use these
> y-x banded rectangles to generate triangle fans, resulting in more
> geometry than strictly necessary to draw the screen.
> 
> This patch combines the bands to reduce geometry for complex scenes.
> ---
>  src/gl-renderer.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 64 insertions(+), 3 deletions(-)
> 
> diff --git a/src/gl-renderer.c b/src/gl-renderer.c
> index 076c242..40447c7 100644
> --- a/src/gl-renderer.c
> +++ b/src/gl-renderer.c
> @@ -25,6 +25,7 @@
>  #include <GLES2/gl2.h>
>  #include <GLES2/gl2ext.h>
>  
> +#include <stdbool.h>
>  #include <stdlib.h>
>  #include <string.h>
>  #include <ctype.h>
> @@ -296,6 +297,55 @@ calculate_edges(struct weston_view *ev, pixman_box32_t *rect,
>  	return n;
>  }
>  
> +static bool
> +merge_down(pixman_box32_t *a, pixman_box32_t *b, pixman_box32_t *merge)
> +{
> +	if (a->x1 == b->x1 && a->x2 == b->x2 && a->y1 == b->y2) {
> +		merge->x1 = a->x1;
> +		merge->x2 = a->x2;
> +		merge->y1 = b->y1;
> +		merge->y2 = a->y2;
> +		return true;
> +	}
> +	return false;
> +}
> +
> +static int
> +compress_bands(pixman_box32_t *inrects, int nrects,
> +		   pixman_box32_t **outrects)
> +{
> +	bool merged;
> +	pixman_box32_t *out, merge_rect;
> +	int i, j, nout;
> +
> +	if (!nrects) {
> +		*outrects = NULL;
> +		return 0;
> +	}
> +
> +	/* nrects is an upper bound - we're not too worried about
> +	 * allocating a little extra
> +	 */
> +	out = malloc(sizeof(pixman_box32_t) * nrects);
> +	out[0] = inrects[0];
> +	nout = 1;
> +	for (i = 1; i < nrects; i++) {
> +		for (j = 0; j < nout; j++) {
> +			merged = merge_down(&inrects[i], &out[j], &merge_rect);
> +			if (merged) {
> +				out[j] = merge_rect;
> +				break;
> +			}
> +		}
> +		if (!merged) {
> +			out[nout] = inrects[i];
> +			nout++;
> +		}
> +	}
> +	*outrects = out;
> +	return nout;
> +}
> +
>  static int
>  texture_region(struct weston_view *ev, pixman_region32_t *region,
>  		pixman_region32_t *surf_region)
> @@ -306,11 +356,20 @@ texture_region(struct weston_view *ev, pixman_region32_t *region,
>  	GLfloat *v, inv_width, inv_height;
>  	unsigned int *vtxcnt, nvtx = 0;
>  	pixman_box32_t *rects, *surf_rects;
> -	int i, j, k, nrects, nsurf;
> -
> -	rects = pixman_region32_rectangles(region, &nrects);
> +	pixman_box32_t *raw_rects;
> +	int i, j, k, nrects, nsurf, raw_nrects;
> +	bool used_band_compression;
> +	raw_rects = pixman_region32_rectangles(region, &raw_nrects);
>  	surf_rects = pixman_region32_rectangles(surf_region, &nsurf);
>  
> +	if (raw_nrects < 4) {
> +		used_band_compression = false;
> +		nrects = raw_nrects;
> +		rects = raw_rects;
> +	} else {
> +		nrects = compress_bands(raw_rects, raw_nrects, &rects);
> +		used_band_compression = true;
> +	}
>  	/* worst case we can have 8 vertices per rect (ie. clipped into
>  	 * an octagon):
>  	 */
> @@ -369,6 +428,8 @@ texture_region(struct weston_view *ev, pixman_region32_t *region,
>  		}
>  	}
>  
> +	if (used_band_compression)
> +		free(rects);
>  	return nvtx;
>  }
>  

Hi Derek,

could you explain a bit where I can see the effect of this and how
big an improvement it is?


Thanks,
pq