[Mesa-dev] [PATCH 2/2] meta: Don't botch color masks when changing drawbuffers.

[Kenneth Graunke]

Color clears should respect each drawbuffer's color mask state.

Previously, we tried to leave the color mask untouched.  However,
_mesa_meta_drawbuffers_from_bitfield() ended up rebinding all the
color drawbuffers in a different order, so we ended up pairing
drawbuffers with the wrong color mask state.

The new _mesa_meta_drawbuffers_and_colormask() function does the
same job as the old _mesa_meta_drawbuffers_from_bitfield(), but
also rearranges the color mask state to match the new drawbuffer
configuration.

This code was largely ripped off from Gallium's st_Clear code.

This fixes ES31-CTS.draw_buffers_indexed.color_masks, which binds
up to 8 drawbuffers, sets color masks for each, and then calls
glClearBufferfv to clear each buffer individually.  ClearBuffer
causes us to rebind only one drawbuffer, at which point we used
ctx->Color.ColorMask[0] (draw buffer 0's state) for everything.

We could probably delete _mesa_meta_drawbuffers_from_bitfield(),
but I'd rather not think about the i965 fast clear code.  Topi is
rewriting a bunch of that soon anyway, so let's delete it then.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94847
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/common/meta.c | 82 ++++++++++++++++++++++++++++++++++++++----
 1 file changed, 75 insertions(+), 7 deletions(-)

diff --git a/src/mesa/drivers/common/meta.c b/src/mesa/drivers/common/meta.c
index eedfb7c..6dcbc8b 100644
--- a/src/mesa/drivers/common/meta.c
+++ b/src/mesa/drivers/common/meta.c
@@ -1618,6 +1618,79 @@ _mesa_meta_drawbuffers_from_bitfield(GLbitfield bits)
 }
 
 /**
+ * Return if all of the color channels are masked.
+ */
+static inline GLboolean
+is_color_disabled(struct gl_context *ctx, int i)
+{
+   return !ctx->Color.ColorMask[i][0] &&
+          !ctx->Color.ColorMask[i][1] &&
+          !ctx->Color.ColorMask[i][2] &&
+          !ctx->Color.ColorMask[i][3];
+}
+
+/**
+ * Given a bitfield of BUFFER_BIT_x draw buffers, call glDrawBuffers to
+ * set GL to only draw to those buffers.  Also, update color masks to
+ * reflect the new draw buffer ordering.
+ */
+static void
+_mesa_meta_drawbuffers_and_colormask(struct gl_context *ctx, GLbitfield mask)
+{
+   GLenum enums[MAX_DRAW_BUFFERS];
+   GLubyte colormask[MAX_DRAW_BUFFERS][4];
+   int num_bufs = 0;
+
+   /* This function is only legal for color buffer bitfields. */
+   assert((mask & ~BUFFER_BITS_COLOR) == 0);
+
+   /* Make sure we don't overflow any arrays. */
+   assert(_mesa_bitcount(mask) <= MAX_DRAW_BUFFERS);
+
+   enums[0] = GL_NONE;
+
+   for (int i = 0; i < ctx->DrawBuffer->_NumColorDrawBuffers; i++) {
+      int b = ctx->DrawBuffer->_ColorDrawBufferIndexes[i];
+      int colormask_idx = ctx->Extensions.EXT_draw_buffers2 ? i : 0;
+
+      if (b < 0 || !(mask & (1 << b)) || is_color_disabled(ctx, colormask_idx))
+         continue;
+
+      switch (b) {
+      case BUFFER_FRONT_LEFT:
+         enums[num_bufs] = GL_FRONT_LEFT;
+         break;
+      case BUFFER_FRONT_RIGHT:
+         enums[num_bufs] = GL_FRONT_RIGHT;
+         break;
+      case BUFFER_BACK_LEFT:
+         enums[num_bufs] = GL_BACK_LEFT;
+         break;
+      case BUFFER_BACK_RIGHT:
+         enums[num_bufs] = GL_BACK_RIGHT;
+         break;
+      default:
+         assert(b >= BUFFER_COLOR0 && b <= BUFFER_COLOR7);
+         enums[num_bufs] = GL_COLOR_ATTACHMENT0 + (b - BUFFER_COLOR0);
+         break;
+      }
+
+      for (int k = 0; k < 4; k++)
+         colormask[num_bufs][k] = ctx->Color.ColorMask[colormask_idx][k];
+
+      num_bufs++;
+   }
+
+   _mesa_DrawBuffers(num_bufs, enums);
+
+   for (int i = 0; i < num_bufs; i++) {
+      _mesa_ColorMaski(i, colormask[i][0], colormask[i][1],
+                          colormask[i][2], colormask[i][3]);
+   }
+}
+
+
+/**
  * Meta implementation of ctx->Driver.Clear() in terms of polygon rendering.
  */
 static void
@@ -1633,6 +1706,7 @@ meta_clear(struct gl_context *ctx, GLbitfield buffers, bool glsl)
 
    metaSave = (MESA_META_ALPHA_TEST |
 	       MESA_META_BLEND |
+               MESA_META_COLOR_MASK |
 	       MESA_META_DEPTH_TEST |
 	       MESA_META_RASTERIZATION |
 	       MESA_META_SHADER |
@@ -1655,11 +1729,6 @@ meta_clear(struct gl_context *ctx, GLbitfield buffers, bool glsl)
 
    if (buffers & BUFFER_BITS_COLOR) {
       metaSave |= MESA_META_DRAW_BUFFERS;
-   } else {
-      /* We'll use colormask to disable color writes.  Otherwise,
-       * respect color mask
-       */
-      metaSave |= MESA_META_COLOR_MASK;
    }
 
    _mesa_meta_begin(ctx, metaSave);
@@ -1695,7 +1764,7 @@ meta_clear(struct gl_context *ctx, GLbitfield buffers, bool glsl)
    /* GL_COLOR_BUFFER_BIT */
    if (buffers & BUFFER_BITS_COLOR) {
       /* Only draw to the buffers we were asked to clear. */
-      _mesa_meta_drawbuffers_from_bitfield(buffers & BUFFER_BITS_COLOR);
+      _mesa_meta_drawbuffers_and_colormask(ctx, buffers & BUFFER_BITS_COLOR);
 
       /* leave colormask state as-is */
 
@@ -1704,7 +1773,6 @@ meta_clear(struct gl_context *ctx, GLbitfield buffers, bool glsl)
          _mesa_ClampColor(GL_CLAMP_FRAGMENT_COLOR, GL_FALSE);
    }
    else {
-      assert(metaSave & MESA_META_COLOR_MASK);
       _mesa_ColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
    }
 
-- 
2.8.0