glViewportIndexedf

glViewportIndexed: man4/glViewportIndexed.xml

glViewportIndexedf and glViewportIndexedfv specify the parameters for a single viewport. index specifies the index of the viewport to modify. index must be less than the value of GL_MAX_VIEWPORTS. For glViewportIndexedf, x, y, w, and h specify the left, bottom, width and height of the viewport in pixels, respectively. For glViewportIndexedfv, v contains the address of an array of floating point values specifying the left ( x ), bottom ( y ), width ( w ), and height ( h ) of each viewport, in that order. x and y give the location of the viewport's lower left corner, and w and h give the width and height of the viewport, respectively. The viewport specifies the affine transformation of x and y from normalized device coordinates to window coordinates. Let x nd y nd be normalized device coordinates. Then the window coordinates x w y w are computed as follows: x w = x nd + 1 ⁢ width 2 + x y w = y nd + 1 ⁢ height 2 + y The location of the viewport's bottom left corner, given by ( x, y ) is clamped to be within the implementaiton-dependent viewport bounds range. The viewport bounds range [ min, max ] can be determined by calling glGet with argument GL_VIEWPORT_BOUNDS_RANGE. Viewport width and height are silently clamped to a range that depends on the implementation. To query this range, call glGet with argument GL_MAX_VIEWPORT_DIMS. The precision with which the GL interprets the floating point viewport bounds is implementation-dependent and may be determined by querying the impementation-defined constant GL_VIEWPORT_SUBPIXEL_BITS. Calling glViewportIndexedfv is equivalent to calling glViewportArray with first set to index, count set to 1 and v passsed directly. glViewportIndexedf is equivalent to:

void glViewportIndexedf(GLuint index, GLfloat x, GLfloat y, GLfloat w, GLfloat h) {
    const float v[4]  = { x, y, w, h };
    glViewportArrayv(index, 1, v);
}