[Metal] Add cross-platform gamma adjustment for texture rendered into…

… QML

- Adapt the GammaAdjust element from QtGraphicalEffects to work with Metal
- Add shaders from Qt
- Create a Vulkan supported version of the fragment shader
- Generate a shader pack using qsb
- Refactor gamma adjustment QML
- Move to own QML file and locate with ignition/gui/qml
- Move shaders to a private subfolder
- Update resources.qrc
- Replace import QtGraphicalEffects 1.0 with import "qrc:/qml"

Signed-off-by: Rhys Mainwaring <rhys.mainwaring@me.com>

include/ignition/gui/qml/IgnGammaAdjust.qml

@@ -0,0 +1,106 @@
+/*
+ * Copyright (C) 2020 Open Source Robotics Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+*/
+
+/*
+ * IgnGammaAdjust.qml is based upon GammaAdjust.qml from the QtGraphicalEffects
+ * module in Qt 5.15.2 which has the license listed below.
+ * 
+ * The 
+*/
+
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the Qt Graphical Effects module.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick 2.9
+
+Item {
+  id: rootItem
+
+  property variant source
+
+  property real gamma: 1.0
+
+  property bool cached: false
+
+  // Replaces SourceProxy in the QtGraphicalEffects version
+  ShaderEffectSource {
+    id: sourceProxy
+    sourceItem: rootItem.source
+    visible: rootItem.visible
+    smooth: true
+    live: true
+    hideSource: visible
+  }
+
+  // Output
+  ShaderEffectSource {
+    id: cacheItem
+    anchors.fill: parent
+    visible: rootItem.cached
+    smooth: true
+    sourceItem: shaderItem
+    live: true
+    hideSource: visible
+  }
+
+  // Apply the gamma adjustment to the source proxy
+  ShaderEffect {
+    id: shaderItem
+    property variant source: sourceProxy
+    property real gamma: 1.0 / Math.max(rootItem.gamma, 0.0001)
+
+    anchors.fill: parent
+
+    fragmentShader: "qrc:qml/private/shaders/gammaadjust.frag"
+  }
+}

include/ignition/gui/qml/private/gammaadjust.frag

@@ -0,0 +1,19 @@
+#version 440
+
+layout(location = 0) in vec2 qt_TexCoord0;
+layout(location = 0) out vec4 fragColor;
+
+layout(std140, binding = 0) uniform buf {
+  mat4 qt_Matrix;
+  float qt_Opacity;
+  float gamma;
+};
+
+layout(binding = 1) uniform sampler2D source;
+
+void main() {
+  vec4 originalColor = texture(source, qt_TexCoord0);
+  originalColor.rgb = originalColor.rgb / max(1.0/256.0, originalColor.a);
+  vec3 adjustedColor = pow(originalColor.rgb, vec3(gamma));
+  fragColor = vec4(adjustedColor * originalColor.a, originalColor.a) * qt_Opacity;
+}

include/ignition/gui/qml/private/shaders/+glslcore/gammaadjust.frag

@@ -0,0 +1,13 @@
+#version 150 core
+in vec2 qt_TexCoord0;
+uniform float qt_Opacity;
+uniform sampler2D source;
+uniform float gamma;
+out vec4 fragColor;
+
+void main(void) {
+    vec4 originalColor = texture(source, qt_TexCoord0.st);
+    originalColor.rgb = originalColor.rgb / max(1.0/256.0, originalColor.a);
+    vec3 adjustedColor = pow(originalColor.rgb, vec3(gamma));
+    fragColor = vec4(adjustedColor * originalColor.a, originalColor.a) * qt_Opacity;
+}

include/ignition/gui/qml/private/shaders/gammaadjust.frag

@@ -0,0 +1,10 @@
+varying highp vec2 qt_TexCoord0;
+uniform highp float qt_Opacity;
+uniform lowp sampler2D source;
+uniform highp float gamma;
+void main(void) {
+    highp vec4 originalColor = texture2D(source, qt_TexCoord0.st);
+    originalColor.rgb = originalColor.rgb / max(1.0/256.0, originalColor.a);
+    highp vec3 adjustedColor = pow(originalColor.rgb, vec3(gamma));
+    gl_FragColor = vec4(adjustedColor * originalColor.a, originalColor.a) * qt_Opacity;
+}

include/ignition/gui/resources.qrc

@@ -22,5 +22,10 @@
   <file>qml/images/menu.png</file>
   <file>qml/images/export_icon.png</file>
   <file>qml/images/search.svg</file>
+
+  <file>qml/IgnGammaAdjust.qml</file>
+  <file>qml/private/shaders/gammaadjust.frag</file>
+  <file>qml/private/shaders/+glslcore/gammaadjust.frag</file>
+  <file>qml/private/shaders/+qsb/gammaadjust.frag</file>
 </qresource>
 </RCC>

src/plugins/minimal_scene/MinimalScene.qml

@@ -17,7 +17,7 @@
 import QtQuick 2.9
 import QtQuick.Controls 2.0
 import RenderWindow 1.0
-import QtGraphicalEffects 1.0
+import "qrc:/qml"
 
 Rectangle {
   width: 1000
@@ -53,7 +53,7 @@ Rectangle {
   /*
    * Gamma correction for sRGB output. Enabled when engine is set to ogre2
    */
-  GammaAdjust {
+  IgnGammaAdjust {
       anchors.fill: renderWindow
       source: renderWindow
       gamma: 2.4

src/plugins/scene3d/Scene3D.qml

@@ -17,7 +17,7 @@
 import QtQuick 2.9
 import QtQuick.Controls 2.0
 import RenderWindow 1.0
-import QtGraphicalEffects 1.0
+import "qrc:/qml"
 
 Rectangle {
   width: 1000
@@ -53,7 +53,7 @@ Rectangle {
   /*
    * Gamma correction for sRGB output. Enabled when engine is set to ogre2
    */
-  GammaAdjust {
+  IgnGammaAdjust {
       anchors.fill: renderWindow
       source: renderWindow
       gamma: 2.4