glRasterPos

The GL maintains a 3D position in window coordinates. This position, called the raster position, is used to position pixel and bitmap write operations. It is maintained with subpixel accuracy. See glBitmap , glDrawPixels , and glCopyPixels .

The current raster position consists of three window coordinates ( $\mathit{x}$ , $\mathit{y}$ , $\mathit{z}$ ), a clip coordinate value ( $\mathit{w}$ ), an eye coordinate distance, a valid bit, and associated color data and texture coordinates. The $\mathit{w}$ coordinate is a clip coordinate, because $\mathit{w}$ is not projected to window coordinates. glRasterPos4 specifies object coordinates $\mathit{x}$ , $\mathit{y}$ , $\mathit{z}$ , and $\mathit{w}$ explicitly. glRasterPos3 specifies object coordinate $\mathit{x}$ , $\mathit{y}$ , and $\mathit{z}$ explicitly, while $\mathit{w}$ is implicitly set to 1. glRasterPos2 uses the argument values for $\mathit{x}$ and $\mathit{y}$ while implicitly setting $\mathit{z}$ and $\mathit{w}$ to 0 and 1.

The object coordinates presented by glRasterPos are treated just like those of a glVertex command: They are transformed by the current modelview and projection matrices and passed to the clipping stage. If the vertex is not culled, then it is projected and scaled to window coordinates, which become the new current raster position, and the GL_CURRENT_RASTER_POSITION_VALID flag is set. If the vertex is culled, then the valid bit is cleared and the current raster position and associated color and texture coordinates are undefined.

The current raster position also includes some associated color data and texture coordinates. If lighting is enabled, then GL_CURRENT_RASTER_COLOR (in RGBA mode) or GL_CURRENT_RASTER_INDEX (in color index mode) is set to the color produced by the lighting calculation (see glLight , glLightModel , and glShadeModel ). If lighting is disabled, current color (in RGBA mode, state variable GL_CURRENT_COLOR ) or color index (in color index mode, state variable GL_CURRENT_INDEX ) is used to update the current raster color. GL_CURRENT_RASTER_SECONDARY_COLOR (in RGBA mode) is likewise updated.

Likewise, GL_CURRENT_RASTER_TEXTURE_COORDS is updated as a function of GL_CURRENT_TEXTURE_COORDS , based on the texture matrix and the texture generation functions (see glTexGen ). Finally, the distance from the origin of the eye coordinate system to the vertex as transformed by only the modelview matrix replaces GL_CURRENT_RASTER_DISTANCE .

Initially, the current raster position is (0, 0, 0, 1), the current raster distance is 0, the valid bit is set, the associated RGBA color is (1, 1, 1, 1), the associated color index is 1, and the associated texture coordinates are (0, 0, 0, 1). In RGBA mode, GL_CURRENT_RASTER_INDEX is always 1; in color index mode, the current raster RGBA color always maintains its initial value.

The raster position is modified by glRasterPos , glBitmap , and glWindowPos .

When the raster position coordinates are invalid, drawing commands that are based on the raster position are ignored (that is, they do not result in changes to GL state).

Calling glDrawElements or glDrawRangeElements may leave the current color or index indeterminate. If glRasterPos is executed while the current color or index is indeterminate, the current raster color or current raster index remains indeterminate.

To set a valid raster position outside the viewport, first set a valid raster position, then call glBitmap with NULL as the bitmap parameter.

When the extension is supported, there are distinct raster texture coordinates for each texture unit. Each texture unit's current raster texture coordinates are updated by glRasterPos .

GL_INVALID_OPERATION is generated if glRasterPos is executed between the execution of glBegin and the corresponding execution of glEnd .

glGet with argument GL_CURRENT_RASTER_POSITION

glGet with argument GL_CURRENT_RASTER_POSITION_VALID

glGet with argument GL_CURRENT_RASTER_DISTANCE

glGet with argument GL_CURRENT_RASTER_COLOR

glGet with argument GL_CURRENT_RASTER_SECONDARY_COLOR

glGet with argument GL_CURRENT_RASTER_INDEX

glGet with argument GL_CURRENT_RASTER_TEXTURE_COORDS

glBitmap , glCopyPixels , glDrawArrays , glDrawElements , glDrawRangeElements , glDrawPixels , glMultiTexCoord , glTexCoord , glTexGen , glVertex , glWindowPos

Copyright 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/ .