Pixels and Textures

Geb Thomas

Adapted from the OpenGL Programming Guide

Learning ObjectivesLearn how to copy information from the

framebufferLearn what a texture isLearn how to use textures

Copying Framebuffers glReadPixels() - Reads a rectangular array

of pixels from the framebuffer and stores the data in processor memory.

glDrawPixels() - Writes a rectangular array of pixels from data kept in processor memory into the framebuffer at the current raster position specified by glRasterPos*().

ReadPixels void glReadPixels(GLint x, GLint y, GLsizei

width, GLsizei height, GLenum format, GLenum type, GLvoid *pixels); Reads pixel data from the framebuffer rectangle

whose lower-left corner is at (x, y) and whose dimensions are width and height and stores it in the array pointed to by pixels. format indicates the kind of pixel data elements that are read, and type indicates the data type of each element.

Format GL_COLOR_INDEX: A single color index GL_RGB: A red color component, followed by

a green color component, followed by a blue color component

GL_RGBA: A red color component, followed by a green color component, followed by a blue color component, followed by an alpha color component

Data TypeGL_UNSIGNED_BYTE: unsigned 8-bit

integerGL_BYTE: signed 8-bit integerGL_BITMAP: single bits in unsigned 8-

bit integers using the same format as glBitmap()

Texture MappingCreate the textureDecide how to apply the textureEnable texture mappingDraw the scene, providing texture

coordinates

Creating the TextureNormally you read in an image and

create the texture pattern bufferOpenGL does not provide convenient

ways to read in an image, you have to use an external library for this, such as this free library for reading and writing JPEG files.

Decide how to apply the textureDecal?Modify the current colors?Blend with the current colors?Modify the current normals?Repeat at edges, or clip?

Learning ObjectivesLearn how to copy information from the

framebufferLearn what a texture isLearn how to use textures