Creating the Texture Map
If you read my article on loading textures, you know the function glTexImage2D() creates a texture out of an image. There’s a little more work to do to create an OpenGL texture map. I’m going to cover that material in this section.
Texture objects store texture data so you don’t have to call glTexImage2D() every time you want to draw a texture map. Call the function glGenTextures() to create a texture object for the texture map. This function takes two arguments: the number of texture objects to create and either a texture name or a list of names, depending on the number of texture objects created. You normally create one texture object at a time.
GLuint textureName; glGenTextures(1, &textureName);
Because OpenGL works on multiple screen resolutions, a texture is not going to be drawn exactly the same on all computers. Depending on the player’s screen resolution, OpenGL may have to scale a texture to make it look right on the player’s screen. You have to tell OpenGL what to do when it has to magnify or minify a texture. Call the function glTexParameteri(), which sets the values of various OpenGL texture parameters. This function takes three arguments.
- The type of texture, which is normally GL_TEXTURE_2D.
- The name of the parameter. It will be GL_TEXTURE_MAG_FILTER for texture magnification and GL_TEXTURE_MIN_FILTER for texture minification.
- The value of the parameter. For texture magnification and minification there are two possible values: GL_NEAREST and GL_LINEAR. GL_NEAREST is faster while GL_LINEAR looks better.
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
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