mesa: Add new variables in gl_context to store sample layout

SampleMap{2,4,8}x variables are used in later patches to implement
EXT_framebuffer_multisample_blit_scaled extension.

V2: Use integer array instead of a string.
    Bump up the comment.

V3: Use uint8_t type array.

Signed-off-by: Anuj Phogat <[email protected]>
Reviewed-by: Jordan Justen <[email protected]>

1 files changed, 32 insertions, 0 deletions

diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index dd330eab729..5e9453b2fd7 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -3606,6 +3606,38 @@ struct gl_constants
    GLint MaxDepthTextureSamples;
    GLint MaxIntegerSamples;
 
+   /**
+    * GL_EXT_texture_multisample_blit_scaled implementation assumes that
+    * samples are laid out in a rectangular grid roughly corresponding to
+    * sample locations within a pixel. Below SampleMap{2,4,8}x variables
+    * are used to map indices of rectangular grid to sample numbers within
+    * a pixel. This mapping of indices to sample numbers must be initialized
+    * by the driver for the target hardware. For example, if we have the 8X
+    * MSAA sample number layout (sample positions) for XYZ hardware:
+    *
+    *        sample indices layout          sample number layout
+    *            ---------                      ---------
+    *            | 0 | 1 |                      | a | b |
+    *            ---------                      ---------
+    *            | 2 | 3 |                      | c | d |
+    *            ---------                      ---------
+    *            | 4 | 5 |                      | e | f |
+    *            ---------                      ---------
+    *            | 6 | 7 |                      | g | h |
+    *            ---------                      ---------
+    *
+    * Where a,b,c,d,e,f,g,h are integers between [0-7].
+    *
+    * Then, initialize the SampleMap8x variable for XYZ hardware as shown
+    * below:
+    *    SampleMap8x = {a, b, c, d, e, f, g, h};
+    *
+    * Follow the logic for other sample counts.
+    */
+   uint8_t SampleMap2x[2];
+   uint8_t SampleMap4x[4];
+   uint8_t SampleMap8x[8];
+
    /** GL_ARB_shader_atomic_counters */
    GLuint MaxAtomicBufferBindings;
    GLuint MaxAtomicBufferSize;