WJLSideBySideToAnaglyphFilter.h

//
// WJLSideBySideToAnaglyphFilter.h
//
// Copyright (c) 2013 William LaFrance
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//

#import <QuartzCore/CoreImage.h>

@interface WJLSideBySideToAnaglyphFilter : CIFilter {
    CIImage *inputImage;
}

@end

WJLSideBySideToAnaglyphFilter.m

//
// WJLSideBySideToAnaglyphFilter.m
//
// Copyright (c) 2013 William LaFrance
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//

#define STRINGIZE(x) #x
#define STRINGIZE2(x) STRINGIZE(x)
#define KERNEL_STRING(text) @STRINGIZE2(text)

#import "WJLSideBySideToAnaglyphFilter.h"

static CIKernel *filterKernel = nil;

NSString *kernelSource() {
    return KERNEL_STRING(
        kernel vec4 filterKernel(sampler image) {
            vec2 size = samplerSize(image);
            vec2 coord = samplerCoord(image);
            
            // Without these two lines, the anaglyph will be centered in the
            // frame at 1/2 width. I played with numbers until it worked, to be
            // honest.
            coord.x += size.x / 2.0;
            coord.x /= 2.0;
            
            vec4 leftPixel = sample(image, vec2(coord.x - size.x / 4.0, coord.y));
            vec4 rightPixel = sample(image, vec2(coord.x + size.x / 4.0, coord.y));
            
            float red = 0.7 * leftPixel.g + 0.3 * leftPixel.b;
            return vec4(red, rightPixel.g, rightPixel.b, 1);
        }
    );
}

@implementation WJLSideBySideToAnaglyphFilter

+ (void)initialize
{
    [CIFilter registerFilterName:@"WJLSideBySideToAnaglyphFilter"
                     constructor:(id<CIFilterConstructor>) self
                 classAttributes:@{
   kCIAttributeFilterDisplayName:@"3D side by side to anaglyph conversion filter",
    kCIAttributeFilterCategories:@[kCICategoryVideo, kCICategoryColorAdjustment]
     }];
}

- (id)init
{
    self = [super init];
    if (self) {
        if (!filterKernel) {
            NSArray *kernels = [CIKernel kernelsWithString:kernelSource()];
            filterKernel = kernels[0];
        }
    }
    return self;
}

- (CIImage *)outputImage
{
    CIImage *image = [self apply:filterKernel, inputImage, nil];
    return image;
}

+ (CIFilter *)filterWithName:(NSString *)name
{
    return self.new;
}

@end