gallium/util: implement layered framebuffer clear in u_blitter

All bound layers (from first_layer to last_layer) should be cleared.

This uses a vertex shader which outputs gl_Layer = gl_InstanceID, so each
instance goes to a different layer. By rendering a quad and setting
the instance count to the number of layers, it will trivially clear all
layers.

This requires AMD_vertex_shader_layer (or PIPE_CAP_TGSI_VS_LAYER), which only
radeonsi supports at the moment. r600 could do this too. Standard DX11
hardware will have to use a geometry shader though, which has higher overhead.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/gallium/auxiliary/util/u_framebuffer.h b/src/gallium/auxiliary/util/u_framebuffer.h
index a8906623042..0e6c98363a8 100644
--- a/src/gallium/auxiliary/util/u_framebuffer.h
+++ b/src/gallium/auxiliary/util/u_framebuffer.h
@@ -55,6 +55,11 @@ util_framebuffer_min_size(const struct pipe_framebuffer_state *fb,
                           unsigned *width,
                           unsigned *height);
 
+
+extern unsigned
+util_framebuffer_get_num_layers(const struct pipe_framebuffer_state *fb);
+
+
 #ifdef __cplusplus
 }
 #endif