How to get texture u v value?
Author
Hi!
I have a simple question:
I set a texture in 2x2 size.
I want to get the u v value.In fact,it should be 0.0,0.5 and 1.0 in uv
but I got 0.25 and 0.75
Please tell me how to get them or some tip!
thank you! ^_^
my code is:
//////////////////////////////////
//my fragment
void main()
{
float u=gl_TexCoord[0].x;
gl_FragColor =vec4(u,u,u,u);
}
//////////////////////////////////
//texture parameter set
glGenTextures(1, &_iTexture);
glBindTexture(GL_TEXTURE_2D, _iTexture);
glTexParameteri(GL_TEXTURE_RETANGLE_NV, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_RETANGLE_NV, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_RETANGLE_NV, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameteri(GL_TEXTURE_RETANGLE_NV, GL_TEXTURE_WRAP_T, GL_CLAMP);
glTexImage2D(GL_TEXTURE_RETANGLE_NV, 0,GL_FLOAT_RGBA32_NV,_iWidth,_iHeight,0, GL_RGBA, GL_FLOAT, 0);
/////////////////////////////////
//Viewport-Sized Quad = Data Stream Generator
glBegin(GL_QUADS);
{
glTexCoord2f(0, 0); glVertex3f(-1, -1, -0.5f);
glTexCoord2f(1, 0); glVertex3f( 1, -1, -0.5f);
glTexCoord2f(1, 1); glVertex3f( 1, 1, -0.5f);
glTexCoord2f(0, 1); glVertex3f(-1, 1, -0.5f);
}
glEnd();
////////////////////////////////
//1:1 pixel to texture mapping
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(-1, 1, -1, 1);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
////////////////////////////////
Where do you "get" any value at all? Right now, all I can see is some rendering code. What specific spot do you want to "get" the values from?
In OpenGL, both display pixels and texture pixels (texels) are measured with 0,0 at the edge. Thus, the center of a texel is at 0.25 and 0.75 in a two-pixel texture, and the center of a display pixel is at 0.5 and 1.5 in a two-pixel display area. Texture sampling is done at the center of each pixel, so if you draw a rectangle from 0 to 2, it will sample at 0.5 and 1.5.
In OpenGL, both display pixels and texture pixels (texels) are measured with 0,0 at the edge. Thus, the center of a texel is at 0.25 and 0.75 in a two-pixel texture, and the center of a display pixel is at 0.5 and 1.5 in a two-pixel display area. Texture sampling is done at the center of each pixel, so if you draw a rectangle from 0 to 2, it will sample at 0.5 and 1.5.
Author
Thank you for your response!
So if I ues the glReadPixels( 0, 0, 2, 2, GL_RED, GL_FLOAT, array );
I can get two values about the center of the texels.
0.25 and 0.75 .
so if I use the "vec4 c = texture2D(texUnit, texCoord.st);"
I can get the value which is interpolated near two value replacing ,is it
right?
^_^
So if I ues the glReadPixels( 0, 0, 2, 2, GL_RED, GL_FLOAT, array );
I can get two values about the center of the texels.
0.25 and 0.75 .
so if I use the "vec4 c = texture2D(texUnit, texCoord.st);"
I can get the value which is interpolated near two value replacing ,is it
right?
^_^
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