/*
* Copyright 2010 Cliff L. Biffle. All Rights Reserved.
* Use of this source code is governed by the Apache License 2.0,
* which can be found in the LICENSE file.
*/
uniform sampler2D depthTex;
uniform sampler2D colorTex;
/*
* Kinect Projection Correction
*
* Since the Kinect is, fundamentally, a camera, its data has already
* undergone perspective projection. Closer objects seem relatively
* larger, and distant objects seem small. If we left the POV fixed,
* we could simply display the Kinect's raw data using an orthographic
* projection -- but what's the fun in that?
*
* The Kinect's depth output looks a lot like a 16-bit grayscale image.
* Usefully, the depth samples are a function of 1/Z, and we need 1/Z
* during the perspective un-projection.
*
* The CPU provides the Kinect's depth data in a 16-bit luminance
* texture, 640x480 pixels in size. To help us perform the texture
* lookup here, it also provides a canned array of 640x480 vertices,
* each of which has...
* 0 ≤ X, Y ≤ 1.0 - each vertex in the XY plane maps to a single pixel,
* in texel coordinates.
* Z is garbage.
*
* Finally, the CPU uses the texture unit's matrix to pass the
* un-projection matrix.
*/
vec4 kinect_unproject(sampler2D texture, vec4 point) {
vec4 sample = texture2D(texture, point.xy);
vec4 kinectPoint = vec4(point.xy, sample.g, 1.);
return gl_TextureMatrix[0] * kinectPoint;
}
varying vec3 normal;
const float pixelDistanceX = 1. / 640.;
const float pixelDistanceY = 1. / 480.;
/*
* Vertex Shader entry point.
*/
void main() {
vec4 vertex = kinect_unproject(depthTex, gl_Vertex);
// Project the point using GL's perspective settings.
gl_Position = gl_ModelViewProjectionMatrix * vertex;
// Calculate the vertex normal in Kinect-camera space.
vec4 rightVertex = kinect_unproject(depthTex, gl_Vertex + vec4(pixelDistanceX, 0, 0, 0));
vec4 downVertex = kinect_unproject(depthTex, gl_Vertex + vec4(0, pixelDistanceY, 0, 0));
// Convert out of homogeneous space for the cross product.
vec3 right3 = rightVertex.xyz / rightVertex.w;
vec3 down3 = downVertex.xyz / downVertex.w;
vec3 vertex3 = vertex.xyz / vertex.w;
vec3 tangent = down3 - vertex3;
vec3 bitangent = right3 - vertex3;
normal = cross(tangent, bitangent);
// Abuse the color channel to communicate data validity.
if (vertex.z <= 0.) {
gl_FrontColor = vec4(gl_Color.xyz, 0);
} else {
gl_FrontColor = gl_Color;
}
}