Graphics Reference
In-Depth Information
Example 9-1
Generating a Texture Object, Binding It, and Loading Image Data
// Texture object handle
GLuint textureId;
// 2 x 2 Image, 3 bytes per pixel (R, G, B)
GLubyte pixels[4 * 3] =
{
255, 0, 0, // Red
0, 255, 0, // Green
0, 0, 255, // Blue
255, 255, 0 // Yellow
};
// Use tightly packed data
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
// Generate a texture object
glGenTextures(1, &textureId);
// Bind the texture object
glBindTexture(GL_TEXTURE_2D, textureId);
// Load the texture
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 2, 2, 0, GL_RGB,
GL_UNSIGNED_BYTE, pixels);
// Set the filtering mode
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
GL_NEAREST);
In the first part of the code, the
pixels
array is initialized with simple 2 × 2
texture data. The data is composed of unsigned byte RGB triplets that are in
the range [0, 255]. When data is fetched from an 8-bit unsigned byte texture
component in the shader, the values are mapped from the range [0, 255] to
the floating-point range [0.0, 1.0]. Typically, an application would not create
texture data in this simple manner, but rather would load the data from an
image file. This example is provided to demonstrate the use of the API.
Prior to calling
glTexImage2D
, the application makes a call to
glPixelStorei
to set the unpack alignment. When texture data is
uploaded via
glTexImage2D
, the rows of pixels are assumed to be aligned
to the value set for
GL_UNPACK_ALIGNMENT
. By default, this value is 4,
meaning that rows of pixels are assumed to begin on 4-byte boundaries.
