Class NVClipSpaceWScaling


  • public class NVClipSpaceWScaling
    extends java.lang.Object
    Virtual Reality (VR) applications often involve a post-processing step to apply a "barrel" distortion to the rendered image to correct the "pincushion" distortion introduced by the optics in a VR device. The barrel distorted image has lower resolution along the edges compared to the center. Since the original image is rendered at high resolution, which is uniform across the complete image, a lot of pixels towards the edges do not make it to the final post-processed image.

    This extension also provides a mechanism to render VR scenes at a non-uniform resolution, in particular a resolution that falls linearly from the center towards the edges. This is achieved by scaling the "w" coordinate of the vertices in the clip space before perspective divide. The clip space "w" coordinate of the vertices may be offset as of a function of "x" and "y" coordinates as follows:

    
     w' = w + Ax + By

    In the intended use case for viewport position scaling, an application should use a set of 4 viewports, one for each of the 4 quadrants of a Cartesian coordinate system. Each viewport is set to the dimension of the image, but is scissored to the quadrant it represents. The application should specify A and B coefficients of the w-scaling equation above, that have the same value, but different signs, for each of the viewports. The signs of A and B should match the signs of X and Y for the quadrant that they represent such that the value of "w'" will always be greater than or equal to the original "w" value for the entire image. Since the offset to "w", (Ax + By), is always positive and increases with the absolute values of "x" and "y", the effective resolution will fall off linearly from the center of the image to its edges.

    Requires NV_viewport_array or OES_viewport_array.

    • Method Detail

      • glViewportPositionWScaleNV

        public static void glViewportPositionWScaleNV​(int index,
                                                      float xcoeff,
                                                      float ycoeff)
        If VIEWPORT_POSITION_W_SCALE_NV is enabled, the w coordinates for each primitive sent to a given viewport will be scaled as a function of its x and y coordinates using the following equation:
        
         w' = xcoeff * x + ycoeff * y + w;

        The coefficients for "x" and "y" used in the above equation depend on the viewport index, and are controlled by this command.

        The viewport specified by index has its coefficients for "x" and "y" set to the xcoeff and ycoeff values. Specifying these coefficients enables rendering images at a non-uniform resolution, in particular a resolution that falls off linearly from the center towards the edges, which is useful for VR applications. VR applications often involve a post-processing step to apply a "barrel" distortion to the rendered image to correct the "pincushion" distortion introduced by the optics in a VR device. The barrel distorted image, has lower resolution along the edges compared to the center. Since the original image is rendered at high resolution, which is uniform across the complete image, a lot of pixels towards the edges do not make it to the final post-processed image. VR applications may use the w-scaling to minimize the processing of unused fragments. To achieve the intended effect, applications should use a set of 4 viewports one for each of the 4 quadrants of a Cartesian coordinate system. Each viewport is set to the dimension of the image, but is scissored to the quadrant it represents. The application should specify the x and y coefficients of the w-scaling equation above, that have the same value, but different signs, for each of the viewports. The signs of xcoeff and ycoeff should match the signs of X and Y for the quadrant that they represent such that the value of "w'" will always be greater than or equal to the original "w" value for the entire image. Since the offset to "w", (Ax + By), is always positive and increases with the absolute values of "x" and "y", the effective resolution will fall off linearly from the center of the image to its edges.

        Parameters:
        index - the viewport index
        xcoeff - the x coefficient
        ycoeff - the y coefficient