source: trunk/src/opengl/qgraphicsshadereffect.cpp@ 866

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#include "qgraphicsshadereffect_p.h"
#if !defined(QT_OPENGL_ES_1)
#include "qglshaderprogram.h"
#include "gl2paintengineex/qglcustomshaderstage_p.h"
#define QGL_HAVE_CUSTOM_SHADERS 1
#endif
#include <QtGui/qpainter.h>
#include <QtGui/qgraphicsitem.h>
#include <QtGui/private/qgraphicseffect_p.h>

QT_BEGIN_NAMESPACE

/*#
    \class QGraphicsShaderEffect
    \brief The QGraphicsShaderEffect class is the base class for creating
    custom GLSL shader effects in a QGraphicsScene.
    \since 4.6
    \ingroup multimedia
    \ingroup graphicsview-api

    The specific effect is defined by a fragment of GLSL source code
    supplied to setPixelShaderFragment().  This source code must define a
    function with the signature
    \c{lowp vec4 customShader(lowp sampler2D imageTexture, highp vec2 textureCoords)}
    that returns the source pixel value
    to use in the paint engine's shader program.  The shader fragment
    is linked with the regular shader code used by the GL2 paint engine
    to construct a complete QGLShaderProgram.

    The following example shader converts the incoming pixmap to
    grayscale and then applies a colorize operation using the
    \c effectColor value:

    \code
    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"
        "}";
    \endcode

    To use this shader code, it is necessary to define a subclass
    of QGraphicsShaderEffect as follows:

    \code
    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;
    };
    \endcode

    The setUniforms() function is called when the effect is about
    to be used for drawing to give the subclass the opportunity to
    set effect-specific uniform variables.

    QGraphicsShaderEffect is only supported when the GL2 paint engine
    is in use.  When any other paint engine is in use (GL1, raster, etc),
    the drawItem() method will draw its item argument directly with
    no effect applied.

    \sa QGraphicsEffect
*/

static const char qglslDefaultImageFragmentShader[] = "\
    lowp vec4 customShader(lowp sampler2D imageTexture, highp vec2 textureCoords) { \
        return texture2D(imageTexture, textureCoords); \
    }\n";

#ifdef QGL_HAVE_CUSTOM_SHADERS

class QGLCustomShaderEffectStage : public QGLCustomShaderStage
{
public:
    QGLCustomShaderEffectStage
            (QGraphicsShaderEffect *e, const QByteArray& source)
        : QGLCustomShaderStage(),
          effect(e)
    {
        setSource(source);
    }

    void setUniforms(QGLShaderProgram *program);

    QGraphicsShaderEffect *effect;
};

void QGLCustomShaderEffectStage::setUniforms(QGLShaderProgram *program)
{
    effect->setUniforms(program);
}

#endif

class QGraphicsShaderEffectPrivate : public QGraphicsEffectPrivate
{
    Q_DECLARE_PUBLIC(QGraphicsShaderEffect)
public:
    QGraphicsShaderEffectPrivate()
        : pixelShaderFragment(qglslDefaultImageFragmentShader)
#ifdef QGL_HAVE_CUSTOM_SHADERS
          , customShaderStage(0)
#endif
    {
    }

    QByteArray pixelShaderFragment;
#ifdef QGL_HAVE_CUSTOM_SHADERS
    QGLCustomShaderEffectStage *customShaderStage;
#endif
};

/*#
    Constructs a shader effect and attaches it to \a parent.
*/
QGraphicsShaderEffect::QGraphicsShaderEffect(QObject *parent)
    : QGraphicsEffect(*new QGraphicsShaderEffectPrivate(), parent)
{
}

/*#
    Destroys this shader effect.
*/
QGraphicsShaderEffect::~QGraphicsShaderEffect()
{
#ifdef QGL_HAVE_CUSTOM_SHADERS
    Q_D(QGraphicsShaderEffect);
    delete d->customShaderStage;