# gluperspective(3g) [xfree86 man page]

GLUPERSPECTIVE(3G) GLUPERSPECTIVE(3G)NAME

gluPerspective - set up a perspective projection matrixC SPECIFICATION

void gluPerspective( GLdouble fovy, GLdouble aspect, GLdouble zNear, GLdouble zFar ) delim $$PARAMETERS

fovy Specifies the field of view angle, in degrees, in the y direction. aspect Specifies the aspect ratio that determines the field of view in the x direction. The aspect ratio is the ratio of x (width) to y (height). zNear Specifies the distance from the viewer to the near clipping plane (always positive). zFar Specifies the distance from the viewer to the far clipping plane (always positive).DESCRIPTION

gluPerspective specifies a viewing frustum into the world coordinate system. In general, the aspect ratio in gluPerspective should match the aspect ratio of the associated viewport. For example, $ "aspect" ~=~ 2.0 $ means the viewer's angle of view is twice as wide in x as it is in y. If the viewport is twice as wide as it is tall, it displays the image without distortion. The matrix generated by gluPerspective is multiplied by the current matrix, just as if glMultMatrix were called with the generated matrix. To load the perspective matrix onto the current matrix stack instead, precede the call to gluPerspective with a call to glLoadIdentity. Given f defined as follows: f ~=~ cotangent"("{"fovy" over 2}")" The generated matrix is left ( ~~ down 130 { matrix { ccol { {f over "aspect"} above 0 above 0 above 0 } ccol { 0 above f above 0 above 0 } ccol { 0 above 0 above {{"zFar" + "zNear"} over {"zNear" - "zFar"}} above} ccol { 0 above 0 above {{2 * "zFar" * "zNear"} over {"zNear" - "zFar"}} above 0} }} ~~~ right )-1NOTES

Depth buffer precision is affected by the values specified for zNear and zFar. The greater the ratio of zFar to zNear is, the less effec- tive the depth buffer will be at distinguishing between surfaces that are near each other. If $r ~=~ "zFar" over "zNear"$ roughly $log sub 2 r$ bits of depth buffer precision are lost. Because $r$ approaches infinity as zNear approaches 0, zNear must never be set to 0.SEE ALSO

glFrustum(3G), glLoadIdentity(3G), glMultMatrix(3G), gluOrtho2D(3G) GLUPERSPECTIVE(3G)

## Check Out this Related Man Page

GLFRUSTUM(3G) GLFRUSTUM(3G)NAME

glFrustum - multiply the current matrix by a perspective matrixC SPECIFICATION

void glFrustum( GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble zNear, GLdouble zFar )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. zNear, zFar Specify the distances to the near and far depth clipping planes. Both distances must be positive.DESCRIPTION

glFrustum describes a perspective matrix that produces a perspective projection. The current matrix (see glMatrixMode) is multiplied by this matrix and the result replaces the current matrix, as if glMultMatrix were called with the following matrix as its argument: 2 zNear0 A 0 right - left 2 zNear 0------------B 0 top - bottom 0 0 C D 0 0------------0 A = (right + left) / (right - left) B = (top + bottom) / (top - bottom) C = - (zFar + zNear) / (zFar - zNear) D = - (2 zFar zNear) / (zFar - zNear) Typically, the matrix mode is GL_PROJECTION, and (left, bottom, -zNear) and (right, top, -zNear) 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).-1speci- fies the location of the far clipping plane. Both zNear and zFar must be positive. Use glPushMatrix and glPopMatrix to save and restore the current matrix stack.-zFarNOTES

Depth buffer precision is affected by the values specified for zNear and zFar. The greater the ratio of zFar to zNear is, the less effec- tive the depth buffer will be at distinguishing between surfaces that are near each other. If r = zFar / zNear roughly log2(r) bits of depth buffer precision are lost. Because r approaches infinity as zNear approaches 0, zNear must never be set to 0.ERRORS

GL_INVALID_VALUE is generated if zNear or zFar is not positive, or if left = right, or bottom = top. GL_INVALID_OPERATION is generated if glFrustum is executed between the execution of glBegin and the corresponding execution of glEnd.ASSOCIATED GETS

glGet with argument GL_MATRIX_MODE glGet with argument GL_MODELVIEW_MATRIX glGet with argument GL_PROJECTION_MATRIX glGet with argument GL_TEXTURE_MATRIX glGet with argument GL_COLOR_MATRIXSEE ALSO

glOrtho, glMatrixMode, glMultMatrix, glPushMatrix, glViewport GLFRUSTUM(3G)