/*
* Copyright 2010, Google Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/*
* This is a conversion of a conversion of a cg shader from Chrome:
* http://src.chromium.org/viewvc/chrome/trunk/src/o3d/samples/shaders/yuv2rgb.shader
*/
/*
* This shader takes a Y'UV420p image as a single greyscale plane, and
* converts it to RGB by sampling the correct parts of the image, and
* by converting the colorspace to RGB on the fly.
*/
/*
* These represent the image dimensions of the SOURCE IMAGE (not the
* Y'UV420p image). This is the same as the dimensions of the Y'
* portion of the Y'UV420p image. They are set from JavaScript.
*/
uniform float imageWidth;
uniform float imageHeight;
/*
* This is the texture sampler where the greyscale Y'UV420p image is
* accessed.
*/
uniform sampler2D textureSampler;
#if defined (USE_UNIFORM_MATRIX)
uniform mat4 conversion;
#endif
varying vec4 v1;
/**
* Given the texture coordinates, our pixel shader grabs the right
* value from each channel of the source image, converts it from Y'UV
* to RGB, and returns the result.
*
* Each Y texel provides luminance information for one pixel in the image.
* Each U and V texel provides color information for a 2x2 block of pixels.
* The U and V texels are just appended to the Y texels.
*
* For images that have a height divisible by 4, things work out nicely.
* For images that are merely divisible by 2, it's not so nice
* (and YUV420 doesn't work for image sizes not divisible by 2).
*
* Here is a 6x6 image, with the layout of the planes of U and V.
* Notice that the V plane starts halfway through the last scanline
* that has U on it.
*
* 0 +---+---+---+---+---+---+
* | Y0| Y0| Y1| Y1| Y2| Y2|
* +---+---+---+---+---+---+
* | Y0| Y0| Y1| Y1| Y2| Y2|
* +---+---+---+---+---+---+
* | Y3| Y3| Y4| Y4| Y5| Y5|
* +---+---+---+---+---+---+
* | Y3| Y3| Y4| Y4| Y5| Y5|
* +---+---+---+---+---+---+
* | Y6| Y6| Y7| Y7| Y8| Y8|
* +---+---+---+---+---+---+
* | Y6| Y6| Y7| Y7| Y8| Y8|
*2/3 +---+---+---+---+---+---+
* | U0| U1| U2| U3| U4| U5|
* +---+---+---+---+---+---+
*5/6 | U6| U7| U8| V0| V1| V2|
* +---+---+---+---+---+---+
* | V3| V4| V5| V6| V7| V8|
* 1 +---+---+---+---+---+---+
* 0 0.5 1
*
* Here is a 4x4 image, where the U and V planes are nicely split into
* separable blocks.
*
* 0 +---+---+---+---+
* | Y0| Y0| Y1| Y1|
* +---+---+---+---+
* | Y0| Y0| Y1| Y1|
* +---+---+---+---+
* | Y2| Y2| Y3| Y3|
* +---+---+---+---+
* | Y2| Y2| Y3| Y3|
*2/3 +---+---+---+---+
* | U0| U1| U2| U3|
*5/6 +---+---+---+---+
* | V0| V1| V2| V3|
* 1 +---+---+---+---+
* 0 0.5 1
*
* The number in a cell indicates which U and V values map onto
* the cell: Un and Vn are used to color the four 'n' cells. As the
* image is drawn its texture coordinates range from 0 to 1. The 'y'
* coordinate is scaled by 2/3 to map from the Y texels, scaled by 1/6
* and shifted down 2/3 to map from the U texels, and scaled by 1/6
* and shifted down 5/6 to map from the V texels. To map from U or V
* texels the 'x' coordinate is scaled by 1/2 always and shifted right
* 1/2 when needed. For example rows 0 and 1 use left side U texels
* (U0-U2 in the first example) while rows 2 and 3 right side U texels
* (U3-U5 in the first example), and so on for the remaining rows.
* When the image height is a multiple of 4, the 'V side' is the same
* as the 'U side,' otherwise it is opposite.
*/
void main() {
float uside, vside;
// texture origin at top left, vertex origin at bottom left
vec2 t = vec2(v1.x, (1. - v1.y));
// y position in pixels
float ypixel = floor(t.y * imageHeight);
if (mod(ypixel, 4.) < 2.) {
// rows 0-1, U on left side
uside = 0.;
} else {
// rows 2-3, U on right side
uside = .5;
}
if (mod(imageHeight, 4.) == 0.) {
// multiple of 4, V same side as U
vside = uside;
} else {
// assume multiple of 2, V opposite side to U
vside = .5 - uside;
}
// shrink y tex. coord. by 2/3 to cover Y section
vec2 y = t * vec2(1., 2./3.);
// for U and V shrink x tex. coord. by 0.5, y by 1/6
t *= vec2(.5, 1./6.);
// shift to proper side and translate down...
vec2 u = t + vec2(uside, 2./3.); // ...to U section
vec2 v = t + vec2(vside, 5./6.); // ...to V section
float yChannel = texture2D(textureSampler, y).x;
float uChannel = texture2D(textureSampler, u).x;
float vChannel = texture2D(textureSampler, v).x;
/*
* This does the colorspace conversion from Y'UV to RGB as a matrix
* multiply. It also does the offset of the U and V channels from
* [0,1] to [-.5,.5] as part of the transform.
*/
vec4 channels = vec4(yChannel, uChannel, vChannel, 1.0);
#if !defined(USE_UNIFORM_MATRIX)
mat4 conversion = mat4( 1.0, 1.0, 1.0, 0.0,
0.0, -0.344, 1.772, 0.0,
1.402, -0.714, 0.0, 0.0,
-0.701, 0.529, -0.886, 1.0);
#endif
gl_FragColor = conversion * channels;
}