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rtrobin
10-15-2012, 01:28 AM
As I know, OpenGL has highly supported NPOT textures since 3.0. Now I' m facing an bizarre phenomenon that NPOT texture cannot be allocated with precise corresponding data.
Words are plain. My testing code is as below.


glGenTextures(1, &texVoxels);
glBindTexture(GL_TEXTURE_3D, texVoxels);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);

int width = 513;
int height = 513;
int depth = 513;
unsigned char *data = new unsigned char[width*height*depth];
memset(data, 0, sizeof(unsigned char)*width*height*depth);

glTexImage3D(GL_TEXTURE_3D, 0, GL_LUMINANCE8, width, height,depth, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, data);

delete []data;
data = NULL;


As code shown above, I need to allocate an NPOT cubic texture of 2^N +1. But program will exit error on glTexImage3D(). The error, I think, is caused by "the size of data less than the texture needed". Because if I allocate data larger enough, the program will pass.
Could anybody please explain this thing for me? I think it is a hardware-related question. Anyway, how could I use NPOT texture and allocate data like this? Even though when the size of data is larger enough the program passes, I am really not sure about how data exactly corresponds to the texture location then.
PS. My graphic card is quadro fx 4800, which supports OpenGL 3.3.

Best regards.

Dan Bartlett
10-15-2012, 03:03 AM
Pixel rows must be aligned on a 4-byte boundary if you are using OpenGL's initial value for GL_PACK_ALIGNMENT. See http://www.opengl.org/sdk/docs/man/xhtml/glPixelStore.xml

To fix it you could either:
a) set your data to 516x513x513 (513*1 byte/pixel rounded up to next multiple of 4) + only fill the first 513 bytes.
b) call glPixelStorei(GL_PACK_ALIGNMENT, 1), but it could have performance consequences.

rtrobin
10-15-2012, 05:48 AM
Pixel rows must be aligned on a 4-byte boundary if you are using OpenGL's initial value for GL_PACK_ALIGNMENT. See http://www.opengl.org/sdk/docs/man/xhtml/glPixelStore.xml

To fix it you could either:
a) set your data to 516x513x513 (513*1 byte/pixel rounded up to next multiple of 4) + only fill the first 513 bytes.
b) call glPixelStorei(GL_PACK_ALIGNMENT, 1), but it could have performance consequences.

Thanks a lot! I didn' t know this well before.
About performance consequences, will it avoid the influence if I use PBO to upload texture data, compared to directly uploading data?