Fix GL_Buffer_Updates to not rely on exact thumbnail

util/test/tests/GL/GL_Buffer_Updates.py

@@ -30,15 +30,6 @@ def check_capture(self):
 
         rdtest.log.success("Draws are all green")
 
-        # Now save the backbuffer to disk
-        ref_path = rdtest.get_tmp_path('backbuffer.png')
-
-        save_data = rd.TextureSave()
-        save_data.resourceId = tex
-        save_data.destType = rd.FileType.PNG
-
-        self.controller.SaveTexture(save_data, ref_path)
-
         # Open the capture and grab the thumbnail, check that it is all green too (dirty way of verifying we didn't
         # break in-app updates but somehow end up with the right data)
         cap = rd.OpenCaptureFile()
@@ -58,9 +49,33 @@ def check_capture(self):
         with open(tmp_path, 'wb') as f:
             f.write(thumb.data)
 
-        # The original thumbnail should also be identical, since we have the uncompressed extended thumbnail.
+        test_reader = rdtest.png.Reader(filename=tmp_path)
+
+        test_w, test_h, test_data, test_info = test_reader.read()
+
+        box_w = test_w//8
+        rows = test_h//box_w
+
+        offset = box_w//2
+
+        rows_data = list(test_data)
+
+        comps = 4 if test_info['alpha'] else 3
+
+        for row in range(0,rows):
+            y = row * box_w + offset
+
+            row_data = rows_data[y]
+
+            for col in range(0, 8):
+                x = col * box_w + offset
+
+                pixel = (row_data[x * comps + 0]/255, row_data[x * comps + 1]/255,
+                         row_data[x * comps + 2]/255)
 
-        if not rdtest.png_compare(tmp_path, ref_path):
-            raise rdtest.TestFailureException("Reference backbuffer and thumbnail image differ", tmp_path, ref_path)
+                if (not rdtest.value_compare((0.2, 0.2, 0.2), pixel, 1) and
+                    not rdtest.value_compare((0.0, 1.0, 0.0), pixel, 1)):
+                    raise rdtest.TestFailureException(
+                        f"Thumbnail of backbuffer at {x},{y} has bad pixel: {pixel}", tmp_path)
 
-        rdtest.log.success("Thumbnail is identical to reference")
+        rdtest.log.success("Thumbnail is as expected")