meta: Clip src/dest rects in BlitFramebuffer, using the scissor

Fixes piglit's fbo-blit-stretch test on drivers which use the meta path.
(i965: should fix Broadwell, but also fixes Sandybridge/Ivybridge/Haswell
since this test falls off the blorp path now due to format conversion)

V2: Use scissor instead of just mangling the rects, to avoid texcoord
rounding problems. (Thanks Marek)

V3: Rebase on Eric's CTSI meta changes; re-add _mesa_update_state in the
CTSI path so that _mesa_clip_blit sees the correct bounds.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=77414
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
Tested-by: Anuj Phogat <anuj.phogat@gmail.com>

src/mesa/drivers/common/meta.c

@@ -2783,6 +2783,13 @@ copytexsubimage_using_blit_framebuffer(struct gl_context *ctx, GLuint dims,
       goto out;
 
    ctx->Meta->Blit.no_ctsi_fallback = true;
+
+   /* Since we've bound a new draw framebuffer, we need to update
+    * its derived state -- _Xmin, etc -- for BlitFramebuffer's clipping to
+    * be correct.
+    */
+   _mesa_update_state(ctx);
+
    /* We skip the core BlitFramebuffer checks for format consistency, which
     * are too strict for CopyTexImage.  We know meta will be fine with format
     * changes.

src/mesa/drivers/common/meta_blit.c

@@ -33,11 +33,13 @@
 #include "main/enable.h"
 #include "main/enums.h"
 #include "main/fbobject.h"
+#include "main/image.h"
 #include "main/macros.h"
 #include "main/matrix.h"
 #include "main/multisample.h"
 #include "main/objectlabel.h"
 #include "main/readpix.h"
+#include "main/scissor.h"
 #include "main/shaderapi.h"
 #include "main/texobj.h"
 #include "main/texenv.h"
@@ -627,6 +629,15 @@ _mesa_meta_BlitFramebuffer(struct gl_context *ctx,
    const GLint dstH = abs(dstY1 - dstY0);
    const GLint dstFlipX = (dstX1 - dstX0) / dstW;
    const GLint dstFlipY = (dstY1 - dstY0) / dstH;
+
+   struct {
+      GLint srcX0, srcY0, srcX1, srcY1;
+      GLint dstX0, dstY0, dstX1, dstY1;
+   } clip = {
+      srcX0, srcY0, srcX1, srcY1,
+      dstX0, dstY0, dstX1, dstY1
+   };
+
    const GLboolean use_glsl_version = ctx->Extensions.ARB_vertex_shader &&
                                       ctx->Extensions.ARB_fragment_shader;
 
@@ -636,8 +647,31 @@ _mesa_meta_BlitFramebuffer(struct gl_context *ctx,
       goto fallback;
    }
 
-   /* only scissor effects blit so save/clear all other relevant state */
+   /* Clip a copy of the blit coordinates. If these differ from the input
-   _mesa_meta_begin(ctx, ~MESA_META_SCISSOR);
+    * coordinates, then we'll set the scissor.
+    */
+   if (!_mesa_clip_blit(ctx, &clip.srcX0, &clip.srcY0, &clip.srcX1, &clip.srcY1,
+                        &clip.dstX0, &clip.dstY0, &clip.dstX1, &clip.dstY1)) {
+      /* clipped/scissored everything away */
+      return;
+   }
+
+   /* Only scissor affects blit, but we're doing to set a custom scissor if
+    * necessary anyway, so save/clear state.
+    */
+   _mesa_meta_begin(ctx, MESA_META_ALL);
+
+   /* If the clipping earlier changed the destination rect at all, then
+    * enable the scissor to clip to it.
+    */
+   if (clip.dstX0 != dstX0 || clip.dstY0 != dstY0 ||
+       clip.dstX1 != dstX1 || clip.dstY1 != dstY1) {
+      _mesa_set_enable(ctx, GL_SCISSOR_TEST, GL_TRUE);
+      _mesa_Scissor(MIN2(clip.dstX0, clip.dstX1),
+                    MIN2(clip.dstY0, clip.dstY1),
+                    abs(clip.dstX0 - clip.dstX1),
+                    abs(clip.dstY0 - clip.dstY1));
+   }
 
    /* Try faster, direct texture approach first */
    if (mask & GL_COLOR_BUFFER_BIT) {