HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 380

R glReadPixels glReadPixels glReadPixels: read a block of pixels from the frame buffer. C Specification void glReadPixels( GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, GLvoid *pixels) Parameters x, y width, height format type pixels Specify the window coordinates of the first pixel that is read from the frame buffer. This location is the lower left corner of a rectangular block of pixels. Specify the dimensions of the pixel rectangle. width and height of one correspond to a single pixel. Specifies the format of the pixel data. The following symbolic values are accepted: GL_COLOR_INDEX, GL_STENCIL_INDEX, GL_DEPTH_COMPONENT, GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB, GL_RGBA, GL_LUMINANCE, and GL_LUMINANCE_ALPHA. Specifies the data type of the pixel data. Must be one of GL_UNSIGNED_BYTE, GL_BYTE, GL_BITMAP, GL_UNSIGNED_SHORT, GL_SHORT, GL_UNSIGNED_INT, GL_INT, or GL_FLOAT. Returns the pixel data. Description glReadPixels returns pixel data from the frame buffer, starting with the pixel whose lower left corner is at location (x, y), into client memory starting at location pixels. Several parameters control the processing of the pixel data before it is placed into client memory. These parameters are set with three commands: glPixelStore, glPixelTransfer, and glPixelMap. This reference page describes the effects on glReadPixels of most, but not all of the parameters specified by these three commands. glReadPixels returns values from each pixel with lower left corner at (x + i, y + j) for 0 ≥ i < width and 0 ≥ j < height. This pixel is said to be the ith pixel in the jth row. Pixels are returned in row order from the lowest to the highest row, left to right in each row. format specifies the format for the returned pixel values; accepted values are: GL_COLOR_INDEX 380 Chapter 16