1 files changed, 40 insertions, 15 deletions

diff --git a/src/mesa/main/buffers.c b/src/mesa/main/buffers.c
index d8b5f3b1f4a..97f06597581 100644
--- a/src/mesa/main/buffers.c
+++ b/src/mesa/main/buffers.c
@@ -338,13 +338,13 @@ _mesa_DrawBuffersARB(GLsizei n, const GLenum *buffers)
    if (ctx->Driver.DrawBuffers)
       ctx->Driver.DrawBuffers(ctx, n, buffers);
    else if (ctx->Driver.DrawBuffer)
-      ctx->Driver.DrawBuffer(ctx, n>0? buffers[0]:GL_NONE);
+      ctx->Driver.DrawBuffer(ctx, n > 0 ? buffers[0] : GL_NONE);
 }
 
 
 /**
  * Helper function to set the GL_DRAW_BUFFER state in the context and
- * current FBO.
+ * current FBO.  Called via glDrawBuffer(), glDrawBuffersARB()
  *
  * All error checking will have been done prior to calling this function
  * so nothing should go wrong at this point.
@@ -362,6 +362,7 @@ _mesa_drawbuffers(GLcontext *ctx, GLuint n, const GLenum *buffers,
 {
    struct gl_framebuffer *fb = ctx->DrawBuffer;
    GLbitfield mask[MAX_DRAW_BUFFERS];
+   GLboolean newState = GL_FALSE;
 
    if (!destMask) {
       /* compute destMask values now */
@@ -375,34 +376,54 @@ _mesa_drawbuffers(GLcontext *ctx, GLuint n, const GLenum *buffers,
       destMask = mask;
    }
 
+   /*
+    * If n==1, destMask[0] may have up to four bits set.
+    * Otherwise, destMask[x] can only have one bit set.
+    */
    if (n == 1) {
-      GLuint buf, count = 0;
-      /* init to -1 to help catch errors */
-      fb->_ColorDrawBufferIndexes[0] = -1;
-      for (buf = 0; buf < BUFFER_COUNT; buf++) {
-         if (destMask[0] & (1 << buf)) {
-            fb->_ColorDrawBufferIndexes[count] = buf;
-            count++;
+      GLuint count = 0, destMask0 = destMask[0];
+      while (destMask0) {
+         GLint bufIndex = _mesa_ffs(destMask0) - 1;
+         if (fb->_ColorDrawBufferIndexes[count] != bufIndex) {
+            fb->_ColorDrawBufferIndexes[count] = bufIndex;
+            newState = GL_TRUE;
          }
+         count++;
+         destMask0 &= ~(1 << bufIndex);
       }
       fb->ColorDrawBuffer[0] = buffers[0];
-      fb->_NumColorDrawBuffers = count;
+      if (fb->_NumColorDrawBuffers != count) {
+         fb->_NumColorDrawBuffers = count;
+         newState = GL_TRUE;
+      }
    }
    else {
       GLuint buf, count = 0;
       for (buf = 0; buf < n; buf++ ) {
          if (destMask[buf]) {
-            fb->_ColorDrawBufferIndexes[buf] = _mesa_ffs(destMask[buf]) - 1;
+            GLint bufIndex = _mesa_ffs(destMask[buf]) - 1;
+            /* only one bit should be set in the destMask[buf] field */
+            ASSERT(_mesa_bitcount(destMask[buf]) == 1);
+            if (fb->_ColorDrawBufferIndexes[buf] != bufIndex) {
+               fb->_ColorDrawBufferIndexes[buf] = bufIndex;
+               newState = GL_TRUE;
+            }
             fb->ColorDrawBuffer[buf] = buffers[buf];
             count = buf + 1;
          }
          else {
-            fb->_ColorDrawBufferIndexes[buf] = -1;
+            if (fb->_ColorDrawBufferIndexes[buf] != -1) {
+               fb->_ColorDrawBufferIndexes[buf] = -1;
+               newState = GL_TRUE;
+            }
          }
       }
       /* set remaining outputs to -1 (GL_NONE) */
       while (buf < ctx->Const.MaxDrawBuffers) {
-         fb->_ColorDrawBufferIndexes[buf] = -1;
+         if (fb->_ColorDrawBufferIndexes[buf] != -1) {
+            fb->_ColorDrawBufferIndexes[buf] = -1;
+            newState = GL_TRUE;
+         }
          fb->ColorDrawBuffer[buf] = GL_NONE;
          buf++;
       }
@@ -413,11 +434,15 @@ _mesa_drawbuffers(GLcontext *ctx, GLuint n, const GLenum *buffers,
       /* also set context drawbuffer state */
       GLuint buf;
       for (buf = 0; buf < ctx->Const.MaxDrawBuffers; buf++) {
-         ctx->Color.DrawBuffer[buf] = fb->ColorDrawBuffer[buf];
+         if (ctx->Color.DrawBuffer[buf] != fb->ColorDrawBuffer[buf]) {
+            ctx->Color.DrawBuffer[buf] = fb->ColorDrawBuffer[buf];
+            newState = GL_TRUE;
+         }
       }
    }
 
-   ctx->NewState |= _NEW_BUFFERS;
+   if (newState)
+      FLUSH_VERTICES(ctx, _NEW_BUFFERS);
 }