glPixelZoom.3G man page
glPixelZoom — specify the pixel zoom factors
void glPixelZoom(GLfloat xfactor, GLfloat yfactor);
Specify the x and y zoom factors for pixel write operations.
glPixelZoom specifies values for the x and y zoom factors. During the execution of glDrawPixels() or glCopyPixels(), if (xr, yr) is the current raster position, and a given element is in the mth row and nth column of the pixel rectangle, then pixels whose centers are in the rectangle with corners at
(xr + n ⋅ xfactor, yr + m ⋅ yfactor)
(xr + n + 1 ⋅ xfactor, yr + m + 1 ⋅ yfactor)
are candidates for replacement. Any pixel whose center lies on the bottom or left edge of this rectangular region is also modified.
Pixel zoom factors are not limited to positive values. Negative zoom factors reflect the resulting image about the current raster position.
GL_INVALID_OPERATION is generated if glPixelZoom is executed between the execution of glBegin() and the corresponding execution of glEnd().
glGet() with argument GL_ZOOM_X
glGet() with argument GL_ZOOM_Y
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