SkyboxEntity can gamma correct the fragments

This is an opt-in feature, required because dds file tend to need gamma
correction while png probably not.

Change-Id: I9f32d8f23110fb2fd6b11f33a20018907355e986
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

4 files changed, 46 insertions, 1 deletions

diff --git a/src/extras/defaults/qskyboxentity.cpp b/src/extras/defaults/qskyboxentity.cpp
index 85899793c..f955cd5c5 100644
--- a/src/extras/defaults/qskyboxentity.cpp
+++ b/src/extras/defaults/qskyboxentity.cpp
@@ -76,6 +76,7 @@ QSkyboxEntityPrivate::QSkyboxEntityPrivate()
     , m_es2RenderPass(new QRenderPass())
     , m_gl3RenderPass(new QRenderPass())
     , m_mesh(new QCuboidMesh())
+    , m_gammaStrengthParameter(new QParameter(QStringLiteral("gammaStrength"), 0.0f))
     , m_textureParameter(new QParameter(QStringLiteral("skyboxTexture"), m_skyboxTexture))
     , m_posXImage(new QTextureImage())
     , m_posYImage(new QTextureImage())
@@ -145,6 +146,7 @@ void QSkyboxEntityPrivate::init()
     m_effect->addTechnique(m_es2Technique);
 
     m_material->setEffect(m_effect);
+    m_material->addParameter(m_gammaStrengthParameter);
     m_material->addParameter(m_textureParameter);
 
     m_mesh->setXYMeshResolution(QSize(2, 2));
@@ -280,6 +282,29 @@ QString QSkyboxEntity::extension() const
     return d->m_extension;
 }
 
+/*!
+ * Sets the gamma correction enable state to \a enabled.
+ * \since 5.9
+ */
+void QSkyboxEntity::setGammaCorrectEnabled(bool enabled)
+{
+    Q_D(QSkyboxEntity);
+    if (enabled != isGammaCorrectEnabled()) {
+        d->m_gammaStrengthParameter->setValue(enabled ? 1.0f : 0.0f);
+        emit gammaCorrectEnabledChanged(enabled);
+    }
+}
+
+/*!
+ * Indicates if gamma correction is enabled for this skybox.
+ * \since 5.9
+ */
+bool QSkyboxEntity::isGammaCorrectEnabled() const
+{
+    Q_D(const QSkyboxEntity);
+    return !qFuzzyIsNull(d->m_gammaStrengthParameter->value().toFloat());
+}
+
 } // namespace Qt3DExtras
 
 QT_END_NAMESPACE
diff --git a/src/extras/defaults/qskyboxentity.h b/src/extras/defaults/qskyboxentity.h
index ca5cab6f2..cc01ff7bb 100644
--- a/src/extras/defaults/qskyboxentity.h
+++ b/src/extras/defaults/qskyboxentity.h
@@ -54,6 +54,7 @@ class QT3DEXTRASSHARED_EXPORT QSkyboxEntity : public Qt3DCore::QEntity
     Q_OBJECT
     Q_PROPERTY(QString baseName READ baseName WRITE setBaseName NOTIFY baseNameChanged)
     Q_PROPERTY(QString extension READ extension WRITE setExtension NOTIFY extensionChanged)
+    Q_PROPERTY(bool gammaCorrect READ isGammaCorrectEnabled WRITE setGammaCorrectEnabled NOTIFY gammaCorrectEnabledChanged)
 public:
     explicit QSkyboxEntity(Qt3DCore::QNode *parent = nullptr);
     ~QSkyboxEntity();
@@ -64,9 +65,13 @@ public:
     void setExtension(const QString &extension);
     QString extension() const;
 
+    void setGammaCorrectEnabled(bool enabled);
+    bool isGammaCorrectEnabled() const;
+
 Q_SIGNALS:
     void baseNameChanged(const QString &path);
     void extensionChanged(const QString &extension);
+    void gammaCorrectEnabledChanged(bool enabled);
 
 private:
     Q_DECLARE_PRIVATE(QSkyboxEntity)
diff --git a/src/extras/defaults/qskyboxentity_p.h b/src/extras/defaults/qskyboxentity_p.h
index 795d59ab2..ebf89bdbc 100644
--- a/src/extras/defaults/qskyboxentity_p.h
+++ b/src/extras/defaults/qskyboxentity_p.h
@@ -99,6 +99,7 @@ class QSkyboxEntityPrivate : public Qt3DCore::QEntityPrivate
     Qt3DRender::QRenderPass *m_es2RenderPass;
     Qt3DRender::QRenderPass *m_gl3RenderPass;
     QCuboidMesh *m_mesh;
+    Qt3DRender::QParameter *m_gammaStrengthParameter;
     Qt3DRender::QParameter *m_textureParameter;
     Qt3DRender::QTextureImage *m_posXImage;
     Qt3DRender:: QTextureImage *m_posYImage;
diff --git a/src/extras/shaders/gl3/skybox.frag b/src/extras/shaders/gl3/skybox.frag
index 99c8f111b..931e20343 100644
--- a/src/extras/shaders/gl3/skybox.frag
+++ b/src/extras/shaders/gl3/skybox.frag
@@ -4,7 +4,21 @@ in vec3 texCoord0;
 out vec4 fragColor;
 uniform samplerCube skyboxTexture;
 
+// Gamma correction
+uniform float gamma = 2.2;
+
+uniform float gammaStrength;
+
+vec3 gammaCorrect(const in vec3 color)
+{
+    return pow(color, vec3(1.0 / gamma));
+}
+
 void main()
 {
-    fragColor = texture(skyboxTexture, texCoord0);
+    vec4 baseColor = texture(skyboxTexture, texCoord0);
+    vec4 gammaColor = vec4(gammaCorrect(baseColor.rgb), 1.0);
+    // This is an odd way to enable or not gamma correction,
+    // but this is a way to avoid branching until we can generate shaders
+    fragColor = mix(baseColor, gammaColor, gammaStrength);
 }