GPUImage shader crashing with "ERROR: One or more attached shaders not successfully compiled"

Question

我正在尝试基于 this Javascript:

为 GPUImage 构建一个 Vibrance 滤镜

/**
 * @filter       Vibrance
 * @description  Modifies the saturation of desaturated colors, leaving saturated colors unmodified.
 * @param amount -1 to 1 (-1 is minimum vibrance, 0 is no change, and 1 is maximum vibrance)
 */
function vibrance(amount) {
    gl.vibrance = gl.vibrance || new Shader(null, '\
        uniform sampler2D texture;\
        uniform float amount;\
        varying vec2 texCoord;\
        void main() {\
            vec4 color = texture2D(texture, texCoord);\
            float average = (color.r + color.g + color.b) / 3.0;\
            float mx = max(color.r, max(color.g, color.b));\
            float amt = (mx - average) * (-amount * 3.0);\
            color.rgb = mix(color.rgb, vec3(mx), amt);\
            gl_FragColor = color;\
        }\
    ');

    simpleShader.call(this, gl.vibrance, {
        amount: clamp(-1, amount, 1)
    });

    return this;
}

有人认为我应该能够more/less复制粘贴着色器块：

GPUImageVibranceFilter.h

@interface GPUImageVibranceFilter : GPUImageFilter
{
    GLint vibranceUniform;
}

// Modifies the saturation of desaturated colors, leaving saturated colors unmodified.
// Value -1 to 1 (-1 is minimum vibrance, 0 is no change, and 1 is maximum vibrance)
@property (readwrite, nonatomic) CGFloat vibrance;

@end

GPUImageVibranceFilter.m

#import "GPUImageVibranceFilter.h"

#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
NSString *const kGPUImageVibranceFragmentShaderString = SHADER_STRING
(
    uniform sampler2D inputImageTexture;
    uniform float vibrance;
    varying highp vec2 textureCoordinate;
    void main() {
        vec4 color = texture2D(inputImageTexture, textureCoordinate);
        float average = (color.r + color.g + color.b) / 3.0;
        float mx = max(color.r, max(color.g, color.b));
        float amt = (mx - average) * (-vibrance * 3.0);
        color.rgb = mix(color.rgb, vec3(mx), amt);
        gl_FragColor = color;
    }
);
#else
NSString *const kGPUImageVibranceFragmentShaderString = SHADER_STRING
(
    uniform sampler2D inputImageTexture;
    uniform float vibrance;
    varying vec2 textureCoordinate;
    void main() {
        vec4 color = texture2D(inputImageTexture, textureCoordinate);
        float average = (color.r + color.g + color.b) / 3.0;
        float mx = max(color.r, max(color.g, color.b));
        float amt = (mx - average) * (-vibrance * 3.0);
        color.rgb = mix(color.rgb, vec3(mx), amt);
        gl_FragColor = color;
    }
);
#endif

@implementation GPUImageVibranceFilter

@synthesize vibrance = _vibrance;

#pragma mark -
#pragma mark Initialization and teardown

- (id)init;
{
    if (!(self = [super initWithFragmentShaderFromString:kGPUImageVibranceFragmentShaderString]))
    {
        return nil;
    }

    vibranceUniform = [filterProgram uniformIndex:@"vibrance"];
    self.vibrance = 0.0;

    return self;
}

#pragma mark -
#pragma mark Accessors

- (void)setVibrance:(CGFloat)vibrance;
{
    _vibrance = vibrance;

    [self setFloat:_vibrance forUniform:vibranceUniform program:filterProgram];
}

@end

但是无法编译，崩溃：

Failed to compile fragment shader
Program link log: ERROR: One or more attached shaders not successfully compiled
Fragment shader compile log: (null)
Vertex shader compile log: (null)

错误当然很明显，但由于没有使用 OpenGL ES 着色器的经验，我不知道到底是什么问题。

Answer 1

One would think I should be able to more/less copy paste the shader block.

在桌面 GLSL 中可能是这种情况，但在 OpenGL ES 中您不能声明 float 变量（这包括派生自 float 的类型，例如 vec2 或 mat4）而不先设置精度 - 片段着色器中 float 没有预定义的默认精度。

实现保证在片段着色器中支持 mediump 和 lowp 浮点精度。但是，在将 highp 设置为默认值之前，您必须进行检查。

整个问题让我尖叫 "missing precision"，但我真的不知道为什么编译器没有在编译日志中告诉你这个。

复习 4.5.3 Default Precision Qualifiers（第 35-36 页）

关于您使用 `CGFloat` 的附注：

小心使用CGFloat。

根据您的编译目标（主机是 32 位还是 64 位），该类型将是单精度或双精度。如果您将声明为 CGFloat 的内容传递给 GL，请停止 =P

改用 GLfloat，因为它始终是 GL 要求的单精度。

有关详细信息，请参阅 related answer I wrote。

GPUImage shader crashing with "ERROR: One or more attached shaders not successfully compiled"