fglFrustum(3G)
fglFrustum - multiply the current matrix by a perspective matrix
As shipped in IRIX 6.5.19. Last changed in IRIX 6.5.15.
NAME fglFrustum - multiply the current matrix by a perspective matrix FORTRAN SPECIFICATION SUBROUTINE fglFrustum( REAL*4 left, REAL*4 right, REAL*4 bottom, REAL*4 top, REAL*4 near, REAL*4 far ) PARAMETERS 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. DESCRIPTION fglFrustum describes a perspective matrix that produces a perspective projection. The current matrix (see fglMatrixMode) is multiplied by this matrix and the result replaces the current matrix, as if fglMultMatrix were called with the following matrix as its argument: | | | | | | | ____________ | 0 A 0 | right - left | | | ____________ | 0 B 0 | top - bottom | | | 0 0 C D | | | 0 0 -1 0 ____________ A = right - left ____________ B = top - bottom __________ C = - far - near __________ D = - far - near Typically, the matrix mode is GL_PROJECTION, and (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, 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. Use fglPushMatrix and fglPopMatrix to save and restore the current matrix stack. NOTES 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 ____ r = near roughly log (r) bits of depth buffer precision are lost. Because r 2 approaches infinity as near approaches 0, near must never be set to 0. ERRORS GL_INVALID_VALUE is generated if near or far is not positive, or if left = right, or bottom = top. GL_INVALID_OPERATION is generated if fglFrustum is executed between the execution of fglBegin and the corresponding execution of fglEnd. ASSOCIATED GETS fglGet with argument GL_MATRIX_MODE fglGet with argument GL_MODELVIEW_MATRIX fglGet with argument GL_PROJECTION_MATRIX fglGet with argument GL_TEXTURE_MATRIX fglGet with argument GL_COLOR_MATRIX SEE ALSO fglOrtho, fglMatrixMode, fglMultMatrix, fglPushMatrix, fglViewport