Gl.RasterPosi (gb.opengl)

Specify the raster position for pixel operations.

Parameters

x, y, z, w

Specify the $\mathit{x}$, $\mathit{y}$, $\mathit{z}$, and $\mathit{w}$ object coordinates (if present) for the raster position.

Parameters

v

Specifies a pointer to an array of two, three, or four elements, specifying $\mathit{x}$, $\mathit{y}$, $\mathit{z}$, and $\mathit{w}$ coordinates, respectively.

Description

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 Gl.Bitmap, Gl.DrawPixels, and Gl.CopyPixels.

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. Gl.RasterPos4 specifies object coordinates $\mathit{x}$, $\mathit{y}$, $\mathit{z}$, and $\mathit{w}$ explicitly. Gl.RasterPos3 specifies object coordinate $\mathit{x}$, $\mathit{y}$, and $\mathit{z}$ explicitly, while $\mathit{w}$ is implicitly set to 1. Gl.RasterPos2 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 Gl.RasterPos are treated just like those of a Gl.Vertex 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 Gl.Light, Gl.LightModel, and Gl.ShadeModel). 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 Gl.TexGen). 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.

Notes

The raster position is modified by Gl.RasterPos, Gl.Bitmap, and Gl.WindowPos.

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 Gl.DrawElements or Gl.DrawRangeElements may leave the current color or index indeterminate. If Gl.RasterPos 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 Gl.Bitmap with NULL as the bitmap parameter.

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

Errors

Gl.INVALID_OPERATION is generated if Gl.RasterPos is executed between the execution of Gl.Begin and the corresponding execution of Gl.End.

Associated Gets

Gl.Get with argument Gl.CURRENT_RASTER_POSITION

Gl.Get with argument Gl.CURRENT_RASTER_POSITION_VALID

Gl.Get with argument Gl.CURRENT_RASTER_DISTANCE

Gl.Get with argument Gl.CURRENT_RASTER_COLOR

Gl.Get with argument Gl.CURRENT_RASTER_SECONDARY_COLOR

Gl.Get with argument Gl.CURRENT_RASTER_INDEX

Gl.Get with argument Gl.CURRENT_RASTER_TEXTURE_COORDS

See also

See original documentation on OpenGL website