[Mesa-dev] [PATCH v2] getteximage: assume texture image is empty for non defined levels

[Juan A. Suarez Romero]

Current code is returning an INVALID_OPERATION when trying to use
getTextureImage() on a level that has not been explicitly defined.

That is, we define a mipmapped Texture2D with 3 levels, and try to use
GetTextureImage() for the 4th levels, and INVALID_OPERATION is returned.

Nevertheless, such case is not listed as an error in OpenGL 4.6 spec,
section 8.11.4 ("Texture Image Queries"), where all the case errors for
this function are defined. So it seems this is a valid operation.

On the other hand, in section 8.22 ("Texture State and Proxy State") it
states:

  "Each initial texture image is null. It has zero width, height, and
   depth, internal format RGBA, or R8 for buffer textures, component
   sizes set to zero and component types set to NONE, the compressed
   flag set to FALSE, a zero compressed size, and the bound buffer
   object name is zero."

We can assume that we are reading this initialized empty image when
calling GetTextureImage() with a non defined level.

With this assumption, we will reach one of the other error cases defined
for the functions. At the end, this means that we will return a
different error to the caller.

This fixes arb_get_texture_sub_image piglit tests.

v2: just return INVALID_VALUE if there isno defined level (Iago)

Signed-off-by: Juan A. Suarez Romero <jasuarez at igalia.com>
---
 src/mesa/main/texgetimage.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/mesa/main/texgetimage.c b/src/mesa/main/texgetimage.c
index 85d0ffd4770..69521c5dd05 100644
--- a/src/mesa/main/texgetimage.c
+++ b/src/mesa/main/texgetimage.c
@@ -1004,8 +1004,31 @@ dimensions_error_check(struct gl_context *ctx,
 
    texImage = select_tex_image(texObj, target, level, zoffset);
    if (!texImage) {
-      /* missing texture image */
-      _mesa_error(ctx, GL_INVALID_OPERATION, "%s(missing image)", caller);
+      /* Trying to return a non-defined level is a valid operation per se, as
+       * OpenGL 4.6 spec, section 8.11.4 ("Texture Image Queries") does not
+       * handle this case as an error.
+       *
+       * Rather, we need to look at section 8.22 ("Texture State and Proxy
+       * State"):
+       *
+       *   "Each initial texture image is null. It has zero width, height, and
+       *    depth, internal format RGBA, or R8 for buffer textures, component
+       *    sizes set to zero and component types set to NONE, the compressed
+       *    flag set to FALSE, a zero compressed size, and the bound buffer
+       *    object name is zero."
+       *
+       * This means we need to assume the image for the non-defined level is
+       * an empty image. With this assumption, we can go back to section
+       * 8.11.4 and checking again the errors:
+       *
+       *   "An INVALID_VALUE error is generated if xoffset + width is greater
+       *    than the texture’s width, yoffset + height is greater than the
+       *    texture’s height, or zoffset + depth is greater than the texture’s
+       *    depth."
+       *
+       * Thus why we return INVALID_VALUE.
+       */
+      _mesa_error(ctx, GL_INVALID_VALUE, "%s(missing image)", caller);
       return true;
    }
 
-- 
2.14.3