On Tue, Sep 4, 2012 at 2:59 PM, Eric Anholt <e...@anholt.net> wrote:
> Stéphane Marchesin <marc...@chromium.org> writes:
>
>> The current computation for the lastlevel is based on the level size and can
>> lead to writing past the end of the texture array. Instead we clamp it by
>> MAX_TEXTURE_LEVELS.
>> ---
>> src/mesa/drivers/dri/intel/intel_tex_image.c | 5 +++++
>> 1 files changed, 5 insertions(+), 0 deletions(-)
>>
>> diff --git a/src/mesa/drivers/dri/intel/intel_tex_image.c
>> b/src/mesa/drivers/dri/intel/intel_tex_image.c
>> index fe9040c..7ef258b 100644
>> --- a/src/mesa/drivers/dri/intel/intel_tex_image.c
>> +++ b/src/mesa/drivers/dri/intel/intel_tex_image.c
>> @@ -88,6 +88,11 @@ intel_miptree_create_for_teximage(struct intel_context
>> *intel,
>> lastLevel = firstLevel;
>> } else {
>> lastLevel = firstLevel + _mesa_logbase2(MAX2(MAX2(width, height),
>> depth));
>> + /* We tried to guess the last level based on the texture size, make
>> + * sure we don't go past MAX_TEXTURE_LEVELS since it's hardcoded
>> + * in many places.
>> + */
>> + lastLevel = MIN2(lastLevel, MAX_TEXTURE_LEVELS - 1);
>> }
>> }
>
> I'm confused. MAX_TEXTURE_LEVELS should set such that it covers
> something from the texture size limits down to 1x1. Does it not?
>
Let's say the app calls glTexImage for level 6, and width = 2048. That
goes through the other layers just fine. Then run that bit of code
(which is kindof funny in how it assumes that if you have a 1 for a
texture dimension, that dimension is unused, so it's also broken but
not the point here):
/* Figure out image dimensions at start level. */
for (i = intelImage->base.Base.Level; i > firstLevel; i--) {
width <<= 1;
if (height != 1)
height <<= 1;
if (depth != 1)
depth <<= 1;
}
You get something insane like width = 2048 * 2^6 so 2^17
Then run that code:
lastLevel = firstLevel + _mesa_logbase2(MAX2(MAX2(width,
height), depth));
Width is the biggest dimension so at that point log2(width) is 17.
That max level will get passed down the stack.
Stéphane
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