gallium: Change PIPE_CAP_TGSI_FS_FBFETCH bool to PIPE_CAP_FBFETCH count

TGSI's FBFETCH instruction currently only supports reading from a single
render target, but NIR intrinsics can support multiple render targets.

radeonsi can only support fetching from RT 0, but other drivers may be
able to support fetching from any render target.

To express this, this patch renames PIPE_CAP_TGSI_FS_FBFETCH to simply
PIPE_CAP_FBFETCH, and converts it from a boolean "is FBFETCH supported?"
to an integer number of render targets which can be fetched.

Reviewed-by: Marek Olšák <[email protected]>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/gallium/docs/source/screen.rst b/src/gallium/docs/source/screen.rst
index c678ac91527..054939f6887 100644
--- a/src/gallium/docs/source/screen.rst
+++ b/src/gallium/docs/source/screen.rst
@@ -378,8 +378,10 @@ The integer capabilities:
 * ``PIPE_CAP_GLSL_OPTIMIZE_CONSERVATIVELY``: Tell the GLSL compiler to use
   the minimum amount of optimizations just to be able to do all the linking
   and lowering.
-* ``PIPE_CAP_TGSI_FS_FBFETCH``: Whether a fragment shader can use the FBFETCH
-  opcode to retrieve the current value in the framebuffer.
+* ``PIPE_CAP_FBFETCH``: The number of render targets whose value in the
+  current framebuffer can be read in the shader.  0 means framebuffer fetch
+  is not supported.  1 means that only the first render target can be read,
+  and a larger value would mean that multiple render targets are supported.
 * ``PIPE_CAP_TGSI_MUL_ZERO_WINS``: Whether TGSI shaders support the
   ``TGSI_PROPERTY_MUL_ZERO_WINS`` shader property.
 * ``PIPE_CAP_DOUBLES``: Whether double precision floating-point operations