Add possibility to mirror ShaderEffectSource generated textures

Using textures generated by ShaderEffectSource items (or Item.layer)
with custom OpenGL code was non-intuitive due to mismatching coordinate
systems, so added a possibility to control the generated texture
orientation.

[ChangeLog][QtQuick][ShaderEffectSource] Added possibility to mirror
generated OpenGL texture.

Change-Id: I7c03d8b6fbfc43d69812c15d244200fb8e7c7bb9
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

3 files changed, 254 insertions, 1 deletions

diff --git a/tests/auto/quick/qquickitemlayer/data/TextureMirroring.qml b/tests/auto/quick/qquickitemlayer/data/TextureMirroring.qml
new file mode 100644
index 0000000000..2827960153
--- /dev/null
+++ b/tests/auto/quick/qquickitemlayer/data/TextureMirroring.qml
@@ -0,0 +1,159 @@
+import QtQuick 2.6
+
+Item
+{
+    width: 250
+    height: 50
+
+    property int mirroring: 0
+
+    // Layered box without effect. Mirroring should not affect how it looks.
+    Rectangle {
+        x: 0
+        y: 0
+        width: 50
+        height: 50
+        layer.enabled: true
+        layer.textureMirroring: mirroring
+        Rectangle {
+            x: 0
+            y: 0
+            width: 25
+            height: 25
+            color: "#000000"
+        }
+        Rectangle {
+            x: 25
+            y: 0
+            width: 25
+            height: 25
+            color: "#ff0000"
+        }
+        Rectangle {
+            x: 0
+            y: 25
+            width: 25
+            height: 25
+            color: "#00ff00"
+        }
+        Rectangle {
+            x: 25
+            y: 25
+            width: 25
+            height: 25
+            color: "#0000ff"
+        }
+    }
+
+    // Layered box with effect. Mirroring should affect how it looks.
+    Rectangle {
+        id: layeredEffectBox
+        x: 50
+        y: 0
+        width: 50
+        height: 50
+        layer.enabled: true
+        layer.textureMirroring: mirroring
+        layer.samplerName: "source"
+        layer.effect: ShaderEffect {
+            property variant source: layeredEffectBox
+            fragmentShader: "
+                uniform lowp sampler2D source;
+                varying highp vec2 qt_TexCoord0;
+                void main() {
+                    gl_FragColor = texture2D(source, qt_TexCoord0);
+                }"
+
+        }
+
+        Rectangle {
+            x: 0
+            y: 0
+            width: 25
+            height: 25
+            color: "#000000"
+        }
+        Rectangle {
+            x: 25
+            y: 0
+            width: 25
+            height: 25
+            color: "#ff0000"
+        }
+        Rectangle {
+            x: 0
+            y: 25
+            width: 25
+            height: 25
+            color: "#00ff00"
+        }
+        Rectangle {
+            x: 25
+            y: 25
+            width: 25
+            height: 25
+            color: "#0000ff"
+        }
+    }
+
+    // Non-layered source item for ShaderEffectSource. Mirroring should not affect how it looks.
+    Rectangle {
+        id: box2
+        x: 100
+        y: 0
+        width: 50
+        height: 50
+        Rectangle {
+            x: 0
+            y: 0
+            width: 25
+            height: 25
+            color: "#000000"
+        }
+        Rectangle {
+            x: 25
+            y: 0
+            width: 25
+            height: 25
+            color: "#ff0000"
+        }
+        Rectangle {
+            x: 0
+            y: 25
+            width: 25
+            height: 25
+            color: "#00ff00"
+        }
+        Rectangle {
+            x: 25
+            y: 25
+            width: 25
+            height: 25
+            color: "#0000ff"
+        }
+    }
+    // ShaderEffectSource item. Mirroring should not affect how it looks.
+    ShaderEffectSource {
+        id: theSource
+        x: 150
+        y: 0
+        width: 50
+        height: 50
+        sourceItem: box2
+        textureMirroring: mirroring
+    }
+    // ShaderEffect item. Mirroring should affect how it looks.
+    ShaderEffect {
+        x: 200
+        y: 0
+        width: 50
+        height: 50
+        property variant source: theSource
+        fragmentShader: "
+            uniform lowp sampler2D source;
+            varying highp vec2 qt_TexCoord0;
+            void main() {
+                gl_FragColor = texture2D(source, qt_TexCoord0);
+            }"
+    }
+}
diff --git a/tests/auto/quick/qquickitemlayer/qquickitemlayer.pro b/tests/auto/quick/qquickitemlayer/qquickitemlayer.pro
index 999f0cf23d..a087948f6d 100644
--- a/tests/auto/quick/qquickitemlayer/qquickitemlayer.pro
+++ b/tests/auto/quick/qquickitemlayer/qquickitemlayer.pro
@@ -25,5 +25,6 @@ OTHER_FILES += \
     data/DisableLayer.qml \
     data/SamplerNameChange.qml \
     data/ItemEffect.qml \
-    data/RectangleEffect.qml
+    data/RectangleEffect.qml \
+    data/TextureMirroring.qml
 DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0
diff --git a/tests/auto/quick/qquickitemlayer/tst_qquickitemlayer.cpp b/tests/auto/quick/qquickitemlayer/tst_qquickitemlayer.cpp
index 25a75c0580..094b69c07f 100644
--- a/tests/auto/quick/qquickitemlayer/tst_qquickitemlayer.cpp
+++ b/tests/auto/quick/qquickitemlayer/tst_qquickitemlayer.cpp
@@ -87,7 +87,12 @@ private slots:
     void itemEffect();
     void rectangleEffect();
 
+    void textureMirroring_data();
+    void textureMirroring();
+
 private:
+    void mirroringCheck(int mirroring, int x, bool shouldMirror, const QImage &fb);
+
     bool m_isMesaSoftwareRasterizer;
     int m_mesaVersion;
 };
@@ -434,6 +439,94 @@ void tst_QQuickItemLayer::rectangleEffect()
     QCOMPARE(fb.pixel(0, 100), qRgb(0, 0, 0xff));
 }
 
+void tst_QQuickItemLayer::textureMirroring_data()
+{
+    QTest::addColumn<int>("mirroring");
+
+    QTest::newRow("no mirroring") << 0;
+    QTest::newRow("horizontal") << 1;
+    QTest::newRow("vertical") << 2;
+    QTest::newRow("horizontal | vertical") << 3;
+}
+
+void tst_QQuickItemLayer::textureMirroring()
+{
+    QFETCH(int, mirroring);
+
+    QQuickView view;
+    view.setSource(testFileUrl("TextureMirroring.qml"));
+
+    QQuickItem *child = view.contentItem()->childItems().at(0);
+    child->setProperty("mirroring", mirroring);
+
+    view.show();
+
+    QTest::qWaitForWindowExposed(&view);
+
+    QImage fb = view.grabWindow();
+
+    // Mirroring should have no visual effect on layered item without shader effect
+    mirroringCheck(mirroring, 0, false, fb);
+
+    // Mirroring should have visual effect on layered item with shader effect
+    mirroringCheck(mirroring, 50, true, fb);
+
+    // Mirroring should have no visual effect on source item for ShaderEffectSource
+    mirroringCheck(mirroring, 100, false, fb);
+
+    // Mirroring should have no visual effect on ShaderEffectSource item
+    mirroringCheck(mirroring, 150, false, fb);
+
+    // Mirroring should have visual effect on ShaderEffect item itself
+    mirroringCheck(mirroring, 200, true, fb);
+}
+
+void tst_QQuickItemLayer::mirroringCheck(int mirroring, int x, bool shouldMirror, const QImage &fb)
+{
+    int offset = 10;
+    int spacing = 25;
+
+    if (shouldMirror) {
+        switch (mirroring) {
+        case 0: { // No mirroring -> Visually Y gets swapped, X is default
+            QCOMPARE(fb.pixel(x + offset, offset), qRgb(0, 0xff, 0));
+            QCOMPARE(fb.pixel(x + offset + spacing, offset), qRgb(0, 0, 0xff));
+            QCOMPARE(fb.pixel(x + offset, offset + spacing), qRgb(0, 0, 0));
+            QCOMPARE(fb.pixel(x + offset + spacing, offset + spacing), qRgb(0xff, 0, 0));
+            break;
+        }
+        case 1: { // Horizontal mirroring -> Visually both X and Y get swapped, as neither is default
+            QCOMPARE(fb.pixel(x + offset, offset), qRgb(0, 0, 0xff));
+            QCOMPARE(fb.pixel(x + offset + spacing, offset), qRgb(0, 0xff, 0));
+            QCOMPARE(fb.pixel(x + offset, offset + spacing), qRgb(0xff, 0, 0));
+            QCOMPARE(fb.pixel(x + offset + spacing, offset + spacing), qRgb(0, 0, 0));
+            break;
+        }
+        case 2: { // Vertical mirroring -> The default case, nothing gets swapped
+            QCOMPARE(fb.pixel(x + offset, offset), qRgb(0, 0, 0));
+            QCOMPARE(fb.pixel(x + offset + spacing, offset), qRgb(0xff, 0, 0));
+            QCOMPARE(fb.pixel(x + offset, offset + spacing), qRgb(0, 0xff, 0));
+            QCOMPARE(fb.pixel(x + offset + spacing, offset + spacing), qRgb(0, 0, 0xff));
+            break;
+        }
+        case 3: { // Both axes mirrored -> Visually X gets swapped, Y is default
+            QCOMPARE(fb.pixel(x + offset, offset), qRgb(0xff, 0, 0));
+            QCOMPARE(fb.pixel(x + offset + spacing, offset), qRgb(0, 0, 0));
+            QCOMPARE(fb.pixel(x + offset, offset + spacing), qRgb(0, 0, 0xff));
+            QCOMPARE(fb.pixel(x + offset + spacing, offset + spacing), qRgb(0, 0xff, 0));
+            break;
+        }
+        default:
+            qWarning() << "Invalid case!";
+            break;
+        }
+    } else {
+        QCOMPARE(fb.pixel(x + offset, offset), qRgb(0, 0, 0));
+        QCOMPARE(fb.pixel(x + offset + spacing, offset), qRgb(0xff, 0, 0));
+        QCOMPARE(fb.pixel(x + offset, offset + spacing), qRgb(0, 0xff, 0));
+        QCOMPARE(fb.pixel(x + offset + spacing, offset + spacing), qRgb(0, 0, 0xff));
+    }
+}
 
 QTEST_MAIN(tst_QQuickItemLayer)