Add documentation for additive color gradient effect

Task-number: QT3DS-3935
Change-Id: I3752f328177f5b8056ee824d167be6fcb14a17b4
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>
Reviewed-by: Tomi Korpipää <tomi.korpipaa@qt.io>

4 files changed, 69 insertions, 1 deletions

diff --git a/doc/src/10-best-practices/80-effects.qdoc b/doc/src/10-best-practices/80-effects.qdoc
index 6dad4eb4..66706f42 100644
--- a/doc/src/10-best-practices/80-effects.qdoc
+++ b/doc/src/10-best-practices/80-effects.qdoc
@@ -68,6 +68,11 @@ lower in the scene graph will be applied before effects that are above them.
 \row
   \li
       \div {align="center"}
+      \image additive-gradient-icon.png
+      \b {\l{Additive color gradient}}
+      \enddiv
+  \li
+      \div {align="center"}
       \image depth-of-field-icon.png
       \b {\l{Depth of field HQ blur}}
       \enddiv
@@ -81,12 +86,12 @@ lower in the scene graph will be applied before effects that are above them.
       \image gaussian-blur-icon.png
       \b {\l{Gaussian blur}}
       \enddiv
+\row
   \li
       \div {align="center"}
       \image hdr-bloom-tonemap-icon.png
       \b {\l{HDR bloom tonemap}}
       \enddiv
-\row
   \li
       \div {align="center"}
       \image motion-blur-icon.png
diff --git a/doc/src/10-best-practices/additive-gradient.qdoc b/doc/src/10-best-practices/additive-gradient.qdoc
new file mode 100644
index 00000000..9581d342
--- /dev/null
+++ b/doc/src/10-best-practices/additive-gradient.qdoc
@@ -0,0 +1,63 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt 3D Studio.
+**
+** $QT_BEGIN_LICENSE:FDL$
+** 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 Free Documentation License Usage
+** Alternatively, this file may be used under the terms of the GNU Free
+** Documentation License version 1.3 as published by the Free Software
+** Foundation and appearing in the file included in the packaging of
+** this file. Please review the following information to ensure
+** the GNU Free Documentation License version 1.3 requirements
+** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+/*!
+
+\title Additive Color Gradient
+\page additive-color-gradient.html
+\ingroup qt3dstudio-best-practices
+
+This effect adds a full-layer vertical gradient to the scene, then additively blends it with all
+other elements on the layer. Additive blending adds the pixel values of the gradient and the
+layer, making the result lighter. White areas do not change, and black areas are the same color
+as the gradient. In the image below, the effect is applied in the right picture.
+
+\image effects-additive-gradient.png
+
+\section1 Properties
+
+\table
+  \header
+    \li Property
+    \li Description
+  \row
+    \li
+      Top color
+    \li
+      The top color of the gradient.
+  \row
+    \li
+      Bottom color
+    \li
+      The bottom color of the gradient.
+\endtable
+
+\section1 Usage
+
+In the inspector palette, select the top and bottom colors of the gradient.
+
+*/
diff --git a/doc/src/images/additive-gradient-icon.png b/doc/src/images/additive-gradient-icon.png
new file mode 100644
index 00000000..efb7ab70
--- /dev/null
+++ b/doc/src/images/additive-gradient-icon.png
diff --git a/doc/src/images/effects-additive-gradient.png b/doc/src/images/effects-additive-gradient.png
new file mode 100644
index 00000000..99553408
--- /dev/null
+++ b/doc/src/images/effects-additive-gradient.png