OpenGL Buffers
 | Color Buffers
 | stores color values, either RGBA or index, for each pixel
| used for drawing onto window --- only buffer that produces visible results
| separate left and right buffers for stereo viewing
| separate front and back buffers for animation using double-buffering
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| Depth Buffer
| stores depth, or z, value from which color comes for each pixel |
| typically used for determining visible objects |
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| Select Buffer
| stores finite amount of pick information for each pixel rendered |
| pick information is of the following format
 | number of names for object found |
| z value of near intersection |
| z value of far intersection |
| all names, really IDs, for given object selected |
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| typically used for selecting, or picking, objects in scene with mouse |
| works by intersecting ray cast from mouse point with objects in scene
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| Stencil Buffer
| stores single mask value for each pixel rendered |
| typically used for masking irregularly shaped regions of screen, e.g., view from windshield of car |
dissolving floor
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mirror
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| Accumulation Buffer
| stores color values, RGBA only, for each pixel |
| typically used to combine a series of images, or renders, into a final, composite, image |
| works by combining rectangular blocks of colors |
aliased shapes
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averaged, or anti-aliased, shapes
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Selecting Buffers for Reading and Writing
In OpenGL you can draw into nearly any buffer you want. By default, in GLUT_SINGLE
mode, the front buffer is enabled, and in GLUT_DOUBLE mode, the back
buffer is enabled. But you can change this if you want, using glDrawBuffer().
glDrawBuffer(GL_FRONT);
selects the front buffer for drawing/writing, while
glDrawBuffer(GL_BACK);
selects the back buffer.There are similar glReadBuffer(), glClear() call that selects a buffer for
reading.
Examples
| pickdepth.cpp
uses select buffer to pick object based on depth from ray cast into scene through mouse point |
| picksquare.cpp
uses select buffer to pick object based on "hierarchical" name of objects |
| shadow.cpp
uses depth buffer to implement z-buffer algorithm for generating shadows |
| antialias.cpp
uses accumulation buffer to implement sub-pixel sampling averaging for anti-aliasing |
| mirror.cpp
uses stencil, depth, and color buffers to render simplified mirror (assumed to be on the xy plane) |
References
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