[Mesa-dev] [PATCH] meta: Clip src/dest rects in BlitFramebuffer.

[Marek Olšák]

For scaled blits, this is not correct. For example, if you blit a
10x10 texture to another 10x10 texture with horizontal scaling of
1.5x, the X texture coordinate of the rightmost pixel should be
6.666666. Mesa clip blit doesn't return floating-point coordinates of
the source, so you can't use them. You can however take the clipped
destination coordinates and set them as a scissor rectangle, keeping
the original coordinates unmodified. That way, you'll get correct
clipping (in hardware though) with correct source coordinates for
scaled blits.

See st_BlitFramebuffer.

Marek

On Mon, Apr 14, 2014 at 10:20 AM, Chris Forbes <chrisf at ijw.co.nz> wrote:
> Nothing was bothering to clip the blit. If the src rect was partially
> outside the framebuffer, we'd end up picking up more copies of the
> edge texels due to clamping.
>
> Note that this is slight overkill -- we could get away with clipping src
> only, since fragments outside the destination surface will be discarded
> anyway.
>
> Fixes piglit's fbo-blit-stretch test on drivers which use the meta path.
> (i965: should fix Broadwell, but also fixes Sandybridge/Ivybridge/Haswell
> since this test falls off the blorp path now due to format conversion)
>
> Signed-off-by: Chris Forbes <chrisf at ijw.co.nz>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=77414
> ---
>  src/mesa/drivers/common/meta_blit.c | 31 +++++++++++++++++++++++++------
>  1 file changed, 25 insertions(+), 6 deletions(-)
>
> diff --git a/src/mesa/drivers/common/meta_blit.c b/src/mesa/drivers/common/meta_blit.c
> index 31e494f..38d53ef 100644
> --- a/src/mesa/drivers/common/meta_blit.c
> +++ b/src/mesa/drivers/common/meta_blit.c
> @@ -33,6 +33,7 @@
>  #include "main/enable.h"
>  #include "main/enums.h"
>  #include "main/fbobject.h"
> +#include "main/image.h"
>  #include "main/macros.h"
>  #include "main/matrix.h"
>  #include "main/multisample.h"
> @@ -590,12 +591,9 @@ blitframebuffer_texture(struct gl_context *ctx,
>     return true;
>  }
>
> -/**
> - * Meta implementation of ctx->Driver.BlitFramebuffer() in terms
> - * of texture mapping and polygon rendering.
> - */
> -void
> -_mesa_meta_BlitFramebuffer(struct gl_context *ctx,
> +
> +static void
> +_mesa_meta_blit_preclipped(struct gl_context *ctx,
>                             GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1,
>                             GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1,
>                             GLbitfield mask, GLenum filter)
> @@ -804,6 +802,27 @@ fallback:
>     }
>  }
>
> +/**
> + * Meta implementation of ctx->Driver.BlitFramebuffer() in terms
> + * of texture mapping and polygon rendering.
> + */
> +void
> +_mesa_meta_BlitFramebuffer(struct gl_context *ctx,
> +                           GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1,
> +                           GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1,
> +                           GLbitfield mask, GLenum filter)
> +{
> +   if (!_mesa_clip_blit(ctx, &srcX0, &srcY0, &srcX1, &srcY1,
> +                        &dstX0, &dstY0, &dstX1, &dstY1)) {
> +      /* nothing left! */
> +      return;
> +   }
> +
> +   _mesa_meta_blit_preclipped(ctx, srcX0, srcY0, srcX1, srcY1,
> +                              dstX0, dstY0, dstX1, dstY1,
> +                              mask, filter);
> +}
> +
>  void
>  _mesa_meta_glsl_blit_cleanup(struct blit_state *blit)
>  {
> --
> 1.9.1
>
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