Question

I am confused with the internal format related to texture2D() in GLSL and glTexImage2D() in OpenGL, When I use(pay attention to the third and the eighth parameters):

glTexImage2D(GL_TEXTURE_2D, 0,GL_RGBA16F_ARB, WINDOW_SIZE, WINDOW_SIZE, 0, GL_RGBA, 
            GL_FLOAT, floatDataPtr);

I got the nonclampedvalue of sampler2D in the glsl without clamped to [0, 1]:

vec4 nonclampedvalue = texture2D(my16floattex2d, texcoord1);

When I use:

glTexImage2D(GL_TEXTURE_2D, 0,GL_RGBA8, WINDOW_SIZE, WINDOW_SIZE, 0, GL_RGBA, 
            GL_UNSIGNED_BYTE, byteDataPtr);

I got the clampedvalue of sampler2D in the glsl clamped to [0, 1]:

vec4 clampedvalue = texuture2D(myunsignedbytetex2d, texcoord2);

So my questions are this:

1. What value will I get in glsl when invoke the glTexImage2D like this(clamped or not clamped):

   glTexImage2D(GL_TEXTURE_2D, 0,GL_RGBA8, WINDOW_SIZE, WINDOW_SIZE, 0, GL_RGBA, 
          GL_FLOAT, floatDataPtr);
   

2. What value will I get in glsl when invoke the glTexImage2D like this(clamped or not clamped):

   glTexImage2D(GL_TEXTURE_2D, 0,GL_RGBA16F_ARB, WINDOW_SIZE, WINDOW_SIZE, 0, GL_RGBA,
           GL_UNSIGNED_BYTE, byteDataPtr);
   

3. As I can’t find the detailed information in OpenGL official website, What value will be return in the sampler2D texture with different internal format as well as different type(such as GL_FLOAT or GL_UNSIGNED_BYTE mentioned above) of the data passed to the texture when invoke the glTexImage2D()? what’s all the rules?

Does anyone can help?

Answer 1

What value will I get in glsl when invoke the glTexImage2D like this(clamped or not clamped):

This is governed only by the “internal format” parameter. Normalized internal formats are… normalized. They don’t store floating point values; they store integer values which are interpreted as floats. The maximum integer value becomes 1.0 and the minimum becomes 0.0 (or -1.0 if it’s an SNORM format).

As I can’t find the detailed information in OpenGL official website

Look harder next time; it’s right there on the Wiki. The “internal format” used for creating textures and renderbuffers. It even explains that the last three parameters govern pixel transfer operations: uploading data to the image.