GPUImage two-pass filter - second frag shader never runs?

Question

It's my impression (and the answer to this question seems to confirm it) that I can subclass from GPUImageTwoPassFilter to effectively run two fragment shaders in succession on an image but keep all the code and such confined into a single class. However, in my experimentation, it doesn't appear that the second fragment shader is ever compiled, much less executed; the example below builds and runs without complaint. The resulting image looks the same as if only the first fragment shader were run in a single-shader class.

What could be going wrong here? It doesn't help that all the examples I can find in the GPUImage code base that subclass GPUImageTwoPassFilter are simply using the same fragment shader program for each pass (as in GPUImageGaussianBlurFilter).

#import "BFTwoPassTest.h"

NSString *const kBFTwoPassTestFirstFragmentShaderString = SHADER_STRING
(
 varying highp vec2 textureCoordinate;
 uniform sampler2D inputImageTexture;

 void main()
 {
     lowp vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);
     gl_FragColor = vec4(1.0, textureColor.g, textureColor.b, 1.0);
 }
 );


NSString *const kBFTwoPassTestSecondFragmentShaderString = SHADER_STRING
(
 varying highp vec2 textureCoordinate;
 uniform sampler2D inputImageTexture;

 void main()
 {
     This should be an obvious syntax error.
 }
 );


@implementation BFTwoPassTest

- (id)init {
    self = [self initWithFirstStageFragmentShaderFromString:kBFTwoPassTestFirstFragmentShaderString secondStageFragmentShaderFromString:kBFTwoPassTestSecondFragmentShaderString];
    if (self) {

    }
    return self;
}


@end

Answer 1

Oops, there was a bug on line 55 of GPUImageTwoPassFilter.m. The following line:

if (!(self = [self initWithFirstStageVertexShaderFromString:kGPUImageVertexShaderString firstStageFragmentShaderFromString:firstStageFragmentShaderString secondStageVertexShaderFromString:kGPUImageVertexShaderString secondStageFragmentShaderFromString:firstStageFragmentShaderString]))

should have been

if (!(self = [self initWithFirstStageVertexShaderFromString:kGPUImageVertexShaderString firstStageFragmentShaderFromString:firstStageFragmentShaderString secondStageVertexShaderFromString:kGPUImageVertexShaderString secondStageFragmentShaderFromString:secondStageFragmentShaderString]))

Thanks for pointing this out, which should be fixed in the repository now. However, in the future may I suggest posting specific framework issues like this to the GitHub issues page for the project instead of here?