glFrustum - multiply the current matrix by a perspective matrix
void glFrustum( GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble near, GLdouble far )
left, right Specify the coordinates for the left and right vertical clipping planes. bottom, top Specify the coordinates for the bottom and top horizontal clipping planes. near, far Specify the distances to the near and far depth clipping planes. Both distances must be positive.
glFrustum describes a perspective matrix that produces a perspective projection. (left, bottom, -near) and (right, top, -near) specify the points on the near clipping plane that are mapped to the lower left and upper right corners of the window, respectively, assuming that the eye is located at (0, 0, 0). -far specifies the location of the far clipping plane. Both near and far must be positive. The corresponding matrix is | | | 2·near | | ---------- | | right-left 0 A 0 | | | | 0 2·near B 0 | | ---------- | | top-bottom | | 0 0 C D | | | | 0 0 -1 0 | right+left A = ---------- right-left top+bottom B = ---------- top-bottom far+near C = - -------- far-near 2·far·near D = - ---------- far-near The current matrix is multiplied by this matrix with the result replacing the current matrix. That is, if M is the current matrix and F is the frustum perspective matrix, then M is replaced with M·F. Use glPushMatrix and glPopMatrix to save and restore the current matrix stack.
Depth buffer precision is affected by the values specified for near and far. The greater the ratio of far to near is, the less effective the depth buffer will be at distinguishing between surfaces that are near each other. If far r = ---- near roughly log r bits of depth buffer precision are lost. Because r 2 approaches infinity as near approaches zero, near must never be set to zero.
GL_INVALID_VALUE is generated if near or far is not positive. GL_INVALID_OPERATION is generated if glFrustum is executed between the execution of glBegin and the corresponding execution of glEnd.
glGet with argument GL_MATRIX_MODE glGet with argument GL_MODELVIEW_MATRIX glGet with argument GL_PROJECTION_MATRIX glGet with argument GL_TEXTURE_MATRIX
glOrtho, glMatrixMode, glMultMatrix, glPushMatrix, glViewport
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Fri Dec 6 11:18:03 EST 1996
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