qt-everywhere-src-5.14.1/qtbase/src/opengl/doc/snippets/code/src_opengl_qgraphicsshadereffect.cpp

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//! [0]
    static char const colorizeShaderCode[] =
        "uniform lowp vec4 effectColor;\n"
        "lowp vec4 customShader(lowp sampler2D imageTexture, highp vec2 textureCoords) {\n"
        "    vec4 src = texture2D(imageTexture, textureCoords);\n"
        "    float gray = dot(src.rgb, vec3(0.212671, 0.715160, 0.072169));\n"
        "    vec4 colorize = 1.0-((1.0-gray)*(1.0-effectColor));\n"
        "    return vec4(colorize.rgb, src.a);\n"
        "}";
//! [0]

//! [1]
    class ColorizeEffect : public QGraphicsShaderEffect
    {
        Q_OBJECT
    public:
        ColorizeEffect(QObject *parent = 0)
            : QGraphicsShaderEffect(parent), color(Qt::black)
        {
            setPixelShaderFragment(colorizeShaderCode);
        }

        QColor effectColor() const { return color; }
        void setEffectColor(const QColor& c)
        {
            color = c;
            setUniformsDirty();
        }

    protected:
        void setUniforms(QGLShaderProgram *program)
        {
            program->setUniformValue("effectColor", color);
        }

    private:
        QColor color;
    };
//! [1]

//! [2]
    lowp vec4 customShader(lowp sampler2D imageTexture, highp vec2 textureCoords) {
        return texture2D(imageTexture, textureCoords);
    }
//! [2]