QDistanceFieldText: QEntity that renders text

A QDistanceFieldText has a text position (within the x/y-plane),
a color, a text (QString), a QFont, and a QDistanceGlyphCache
that is used to retrieve the glyph textures needed for rendering.

To render a given string, we use a QTextLayout to generate GlyphRuns,
which are associated with a given QRawFont. Now the following may
happen:
  1. there may be multiple QRawFonts generated by the QTextLayout.
     this is because some glyphs may not be available in one font,
     so another font has to be used for these glyphs.
  2. for the same QRawFont, multiple QTextureAtlasses may be needed
     for all glyphs. This is because the the QDistanceFieldGlyphCache
     grows lazily by allocating more QTextureAtlasses on demand.

So, for any given QDistanceFieldText, we might need to use multiple
textures for rendering. Because of this, we might need to create multiple
QEntities, each with a separate QDistanceFieldMaterial.

These QEntities are the DistanceFieldTextRenderers, which encapsulate
all QComponents needed to render the glyphs taken from one texture.

When something changes, QDistanceFieldText::update() uses a QTextLayout
to generate a number of QGlyphRuns, each associated with a QRawFont.

These QGlyphRuns are then given to
QDistanceFieldTextPrivate::setCurrentGlyphRuns(). There, for each distinct
texture, all glyph positions are gathered, and according vertex and index
buffers are built. These index buffers are then given to the
DistanceFieldTextRenderer nodes. We make sure to properly ref-count the
glyphs within the QDistanceFieldGlyphCache.

Change-Id: Icf332b87541a6426abd4fbb12e2968a6d8ec5c4c
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

1 files changed, 90 insertions, 0 deletions

diff --git a/src/extras/text/distancefieldtextrenderer_p.h b/src/extras/text/distancefieldtextrenderer_p.h
new file mode 100644
index 000000000..fdb9a836f
--- /dev/null
+++ b/src/extras/text/distancefieldtextrenderer_p.h
@@ -0,0 +1,90 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 Klaralvdalens Datakonsult AB (KDAB).
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the Qt3D module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QT3DEXTRAS_DISTANCEFIELDTEXTRENDERER_P_H
+#define QT3DEXTRAS_DISTANCEFIELDTEXTRENDERER_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists for the convenience
+// of other Qt classes.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtCore/QRectF>
+#include <Qt3DCore/qnode.h>
+#include <Qt3DCore/qentity.h>
+#include <Qt3DExtras/qt3dextras_global.h>
+
+QT_BEGIN_NAMESPACE
+
+namespace Qt3DRender {
+class QAbstractTexture;
+}
+
+namespace Qt3DExtras {
+
+class DistanceFieldTextRendererPrivate;
+
+class DistanceFieldTextRenderer : public Qt3DCore::QEntity
+{
+    Q_OBJECT
+
+public:
+    DistanceFieldTextRenderer(Qt3DCore::QNode *parent = nullptr);
+    ~DistanceFieldTextRenderer();
+
+    void setGlyphData(Qt3DRender::QAbstractTexture *glyphTexture,
+                      const QVector<float> &vertexData,
+                      const QVector<quint16> &indexData);
+
+    void setColor(const QColor &color);
+
+    Q_DECLARE_PRIVATE(DistanceFieldTextRenderer)
+};
+
+} // namespace Qt3DExtras
+
+QT_END_NAMESPACE
+
+#endif // QT3DEXTRAS_DISTANCEFIELDTEXTRENDERER_P_H