Implement support for 16bpc image formats

Adds support for 16bit per color image formats in QImage. This makes it
possible to read and write 16bpc PNGs, and take full advantage of the
16bpc paint engine.

[ChangeLog][QtGui][QImage] QImage now supports 64bit image formats with
16 bits per color channel, compatible with 16bpc PNG or RGBA16 OpenGL
formats.

Task-number: QTBUG-45858
Change-Id: Icd28bd5868a6efcf65cb5bd56031d42941e04099
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

3 files changed, 43 insertions, 1 deletions

diff --git a/src/gui/opengl/qopenglframebufferobject.cpp b/src/gui/opengl/qopenglframebufferobject.cpp
index 21ed029dfc..400888cc21 100644
--- a/src/gui/opengl/qopenglframebufferobject.cpp
+++ b/src/gui/opengl/qopenglframebufferobject.cpp
@@ -106,6 +106,10 @@ QT_BEGIN_NAMESPACE
 #define GL_RGB10                          0x8052
 #endif
 
+#ifndef GL_RGB16
+#define GL_RGB16                          0x8054
+#endif
+
 #ifndef GL_RGBA8
 #define GL_RGBA8                          0x8058
 #endif
@@ -114,6 +118,10 @@ QT_BEGIN_NAMESPACE
 #define GL_RGB10_A2                       0x8059
 #endif
 
+#ifndef GL_RGBA16
+#define GL_RGBA16                         0x805B
+#endif
+
 #ifndef GL_BGRA
 #define GL_BGRA                           0x80E1
 #endif
@@ -127,6 +135,7 @@ QT_BEGIN_NAMESPACE
 #endif
 
 
+
 /*!
     \class QOpenGLFramebufferObjectFormat
     \brief The QOpenGLFramebufferObjectFormat class specifies the format of an OpenGL
@@ -522,6 +531,8 @@ void QOpenGLFramebufferObjectPrivate::initTexture(int idx)
     GLuint pixelType = GL_UNSIGNED_BYTE;
     if (color.internalFormat == GL_RGB10_A2 || color.internalFormat == GL_RGB10)
         pixelType = GL_UNSIGNED_INT_2_10_10_10_REV;
+    else if (color.internalFormat == GL_RGB16  || color.internalFormat == GL_RGBA16)
+        pixelType = GL_UNSIGNED_SHORT;
 
     funcs.glTexImage2D(target, 0, color.internalFormat, color.size.width(), color.size.height(), 0,
                        GL_RGBA, pixelType, NULL);
@@ -1304,6 +1315,14 @@ static inline QImage qt_gl_read_framebuffer_rgb10a2(const QSize &size, bool incl
     return img;
 }
 
+static inline QImage qt_gl_read_framebuffer_rgba16(const QSize &size, bool include_alpha, QOpenGLContext *context)
+{
+    // We assume OpenGL 1.2+ or ES 3.0+ here.
+    QImage img(size, include_alpha ? QImage::Format_RGBA64_Premultiplied : QImage::Format_RGBX64);
+    context->functions()->glReadPixels(0, 0, size.width(), size.height(), GL_RGBA, GL_UNSIGNED_SHORT, img.bits());
+    return img;
+}
+
 static QImage qt_gl_read_framebuffer(const QSize &size, GLenum internal_format, bool include_alpha, bool flip)
 {
     QOpenGLContext *ctx = QOpenGLContext::currentContext();
@@ -1318,6 +1337,10 @@ static QImage qt_gl_read_framebuffer(const QSize &size, GLenum internal_format,
         return qt_gl_read_framebuffer_rgb10a2(size, false, ctx).mirrored(false, flip);
     case GL_RGB10_A2:
         return qt_gl_read_framebuffer_rgb10a2(size, include_alpha, ctx).mirrored(false, flip);
+    case GL_RGB16:
+        return qt_gl_read_framebuffer_rgba16(size, false, ctx).mirrored(false, flip);
+    case GL_RGBA16:
+        return qt_gl_read_framebuffer_rgba16(size, include_alpha, ctx).mirrored(false, flip);
     case GL_RGBA:
     case GL_RGBA8:
     default:
@@ -1346,7 +1369,8 @@ Q_GUI_EXPORT QImage qt_gl_read_framebuffer(const QSize &size, bool alpha_format,
     is used only when internalTextureFormat() is set to \c GL_RGB. Since Qt 5.2
     the function will fall back to premultiplied RGBA8888 or RGBx8888 when
     reading to (A)RGB32 is not supported, and this includes OpenGL ES. Since Qt
-    5.4 an A2BGR30 image is returned if the internal format is RGB10_A2.
+    5.4 an A2BGR30 image is returned if the internal format is RGB10_A2, and since
+    Qt 5.12 a RGBA64 image is return if the internal format is RGBA16.
 
     If the rendering in the framebuffer was not done with premultiplied alpha in mind,
     create a wrapper QImage with a non-premultiplied format. This is necessary before
diff --git a/src/gui/opengl/qopenglpaintengine.cpp b/src/gui/opengl/qopenglpaintengine.cpp
index aca57d664a..3680b3c3c2 100644
--- a/src/gui/opengl/qopenglpaintengine.cpp
+++ b/src/gui/opengl/qopenglpaintengine.cpp
@@ -1567,6 +1567,7 @@ void QOpenGL2PaintEngineEx::drawImage(const QRectF& dest, const QImage& image, c
     switch (image.format()) {
     case QImage::Format_RGBA8888:
     case QImage::Format_ARGB32:
+    case QImage::Format_RGBA64:
         d->shaderManager->setSrcPixelType(QOpenGLEngineShaderManager::NonPremultipliedImageSrc);
         bindOption = 0;
         break;
diff --git a/src/gui/opengl/qopengltextureuploader.cpp b/src/gui/opengl/qopengltextureuploader.cpp
index 0204d4852f..fc449d8090 100644
--- a/src/gui/opengl/qopengltextureuploader.cpp
+++ b/src/gui/opengl/qopengltextureuploader.cpp
@@ -61,6 +61,10 @@
 #define GL_RGB10_A2                       0x8059
 #endif
 
+#ifndef GL_RGBA16
+#define GL_RGBA16                         0x805B
+#endif
+
 #ifndef GL_BGRA
 #define GL_BGRA 0x80E1
 #endif
@@ -193,6 +197,15 @@ qsizetype QOpenGLTextureUploader::textureImage(GLenum target, const QImage &imag
         pixelType = GL_UNSIGNED_BYTE;
         targetFormat = image.format();
         break;
+    case QImage::Format_RGBX64:
+    case QImage::Format_RGBA64:
+    case QImage::Format_RGBA64_Premultiplied:
+        externalFormat = internalFormat = GL_RGBA;
+        if (isOpenGL12orBetter || (context->isOpenGLES() && context->format().majorVersion() >= 3))
+            internalFormat = GL_RGBA16;
+        pixelType = GL_UNSIGNED_SHORT;
+        targetFormat =  image.format();
+        break;
     case QImage::Format_Indexed8:
         if (sRgbBinding) {
             // Always needs conversion
@@ -262,11 +275,15 @@ qsizetype QOpenGLTextureUploader::textureImage(GLenum target, const QImage &imag
             targetFormat = QImage::Format_ARGB32_Premultiplied;
         else if (targetFormat == QImage::Format_RGBA8888)
             targetFormat = QImage::Format_RGBA8888_Premultiplied;
+        else if (targetFormat == QImage::Format_RGBA64)
+            targetFormat = QImage::Format_RGBA64_Premultiplied;
     } else {
         if (targetFormat == QImage::Format_ARGB32_Premultiplied)
             targetFormat = QImage::Format_ARGB32;
         else if (targetFormat == QImage::Format_RGBA8888_Premultiplied)
             targetFormat = QImage::Format_RGBA8888;
+        else if (targetFormat == QImage::Format_RGBA64_Premultiplied)
+            targetFormat = QImage::Format_RGBA64;
     }
 
     if (sRgbBinding) {