On 11/23/2011 12:28 AM, zhigang gong wrote:
Hi guys,
I have a question about the internal implementation of glDrawArrays or
any rendering functions.
In the code path, it calls to _mesa_update_texture(), and if there is
really a complete texture,
it will call _mesa_reference_texobj to set it to _Current, and
increase the texture object's reference
counter.
My question is when it will decrease the reference counter? This
implicit increasing seems
causes the reference counter unbalanced, and then will cause
unexpected behaviour. Here is an
example:
1 glGenTextures(1, &tex);
2 glActiveTexture(GL_TEXTURE0);
3 glBindTexture(GL_TEXTURE_2D, tex);
4 glTexImage2D(GL_TEXTURE_2D, 0, iformat,
w, h, 0, format, type, bits);
5 glEnable(GL_TEXTURE_2D);
6 glUseProgram(shader_prog);
7 ... /*setup attribute array here.*/
8 glDrawArray(GL_TRIANGLE_FAN, 0, 4);
9 glUseProgram(0);
10 glDeleteTexture(1, &tex);
At Line 1, tex object is created with reference count initialized to 1.
At Line 3, tex object's reference count increased to 2.
At Line 8, it implicit increases tex object's reference count to 3.
At Line 10, it implict unbinds the tex object which decreases the
count to 2.
then it try to unreference the tex object which
decreases the count to1.
You can see that finally, the tex object's reference's count is 1 not
zero
and thus it will not be freed. This is not what I expected.
Is there any mistakes in my use case? Or anyone can tell me how to
make sure the texture object get freed after the usage of it.
As long as the texture object is still bound to unit 0's
GL_TEXTURE_2D, the texture will not get deleted.
When another texture gets bound to the binding point, the "deleted"
texture's ref count should go to zero and really be deleted. For
example, binding the default texture object should do that:
glBindTexture(GL_TEXTURE_2D, 0);
If this isn't working, can you provide a test program?
-Brian
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