Fix tiling of NPOT textures on GL/ES

The emulation was not working since the vertices are clamped before
getting to the fragment shader. So instead just resize the brush if
not supported.

Change-Id: I856e47890cd3021874b77d869a6ff7162cadde10
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

3 files changed, 20 insertions, 25 deletions

diff --git a/src/gui/opengl/qopenglengineshadermanager.cpp b/src/gui/opengl/qopenglengineshadermanager.cpp
index f66193cb01..b7bac2728a 100644
--- a/src/gui/opengl/qopenglengineshadermanager.cpp
+++ b/src/gui/opengl/qopenglengineshadermanager.cpp
@@ -167,7 +167,7 @@ QOpenGLEngineSharedShaders::QOpenGLEngineSharedShaders(QOpenGLContext* context)
         code[CustomImageSrcFragmentShader] = qopenglslCustomSrcFragmentShader_core; // Calls "customShader", which must be appended
         code[SolidBrushSrcFragmentShader] = qopenglslSolidBrushSrcFragmentShader_core;
 
-        code[TextureBrushSrcFragmentShader] = qopenglslTextureBrushSrcFragmentShader_desktop_core;
+        code[TextureBrushSrcFragmentShader] = qopenglslTextureBrushSrcFragmentShader_core;
         code[TextureBrushSrcWithPatternFragmentShader] = qopenglslTextureBrushSrcWithPatternFragmentShader_core;
         code[PatternBrushSrcFragmentShader] = qopenglslPatternBrushSrcFragmentShader_core;
         code[LinearGradientBrushSrcFragmentShader] = qopenglslLinearGradientBrushSrcFragmentShader_core;
@@ -212,10 +212,7 @@ QOpenGLEngineSharedShaders::QOpenGLEngineSharedShaders(QOpenGLContext* context)
         code[AlphaImageSrcFragmentShader] = qopenglslAlphaImageSrcFragmentShader;
         code[CustomImageSrcFragmentShader] = qopenglslCustomSrcFragmentShader; // Calls "customShader", which must be appended
         code[SolidBrushSrcFragmentShader] = qopenglslSolidBrushSrcFragmentShader;
-        if (context->isOpenGLES())
-            code[TextureBrushSrcFragmentShader] = qopenglslTextureBrushSrcFragmentShader_ES;
-        else
-            code[TextureBrushSrcFragmentShader] = qopenglslTextureBrushSrcFragmentShader_desktop;
+        code[TextureBrushSrcFragmentShader] = qopenglslTextureBrushSrcFragmentShader;
         code[TextureBrushSrcWithPatternFragmentShader] = qopenglslTextureBrushSrcWithPatternFragmentShader;
         code[PatternBrushSrcFragmentShader] = qopenglslPatternBrushSrcFragmentShader;
         code[LinearGradientBrushSrcFragmentShader] = qopenglslLinearGradientBrushSrcFragmentShader;
diff --git a/src/gui/opengl/qopenglengineshadersource_p.h b/src/gui/opengl/qopenglengineshadersource_p.h
index 5d9ee8110b..3ac599b6c2 100644
--- a/src/gui/opengl/qopenglengineshadersource_p.h
+++ b/src/gui/opengl/qopenglengineshadersource_p.h
@@ -303,17 +303,7 @@ static const char* const qopenglslPositionWithTextureBrushVertexShader = "\n\
 static const char* const qopenglslAffinePositionWithTextureBrushVertexShader
                  = qopenglslPositionWithTextureBrushVertexShader;
 
-// OpenGL ES does not support GL_REPEAT wrap modes for NPOT textures. So instead,
-// we emulate GL_REPEAT by only taking the fractional part of the texture coords.
-// TODO: Special case POT textures which don't need this emulation
-static const char* const qopenglslTextureBrushSrcFragmentShader_ES = "\n\
-    varying highp   vec2      brushTextureCoords; \n\
-    uniform         sampler2D brushTexture; \n\
-    lowp vec4 srcPixel() { \n\
-        return texture2D(brushTexture, fract(brushTextureCoords)); \n\
-    }\n";
-
-static const char* const qopenglslTextureBrushSrcFragmentShader_desktop = "\n\
+static const char* const qopenglslTextureBrushSrcFragmentShader = "\n\
     varying   highp   vec2      brushTextureCoords; \n\
     uniform           sampler2D brushTexture; \n\
     lowp vec4 srcPixel() \n\
@@ -795,7 +785,7 @@ static const char* const qopenglslPositionWithTextureBrushVertexShader_core = "\
 static const char* const qopenglslAffinePositionWithTextureBrushVertexShader_core
                  = qopenglslPositionWithTextureBrushVertexShader_core;
 
-static const char* const qopenglslTextureBrushSrcFragmentShader_desktop_core = "\n\
+static const char* const qopenglslTextureBrushSrcFragmentShader_core = "\n\
     in      vec2      brushTextureCoords; \n\
     uniform sampler2D brushTexture; \n\
     vec4 srcPixel() \n\
diff --git a/src/gui/opengl/qopenglpaintengine.cpp b/src/gui/opengl/qopenglpaintengine.cpp
index 5902713faa..aca57d664a 100644
--- a/src/gui/opengl/qopenglpaintengine.cpp
+++ b/src/gui/opengl/qopenglpaintengine.cpp
@@ -272,6 +272,12 @@ GLuint QOpenGL2PaintEngineExPrivate::bindTexture(const ImageWithBindOptions &ima
     return QOpenGLTextureCache::cacheForContext(ctx)->bindTexture(ctx, imageWithOptions.image, imageWithOptions.options);
 }
 
+inline static bool isPowerOfTwo(int x)
+{
+    // Assumption: x >= 1
+    return x == (x & -x);
+}
+
 void QOpenGL2PaintEngineExPrivate::updateBrushTexture()
 {
     Q_Q(QOpenGL2PaintEngineEx);
@@ -304,16 +310,18 @@ void QOpenGL2PaintEngineExPrivate::updateBrushTexture()
         currentBrushImage = currentBrush.textureImage();
 
         int max_texture_size = ctx->d_func()->maxTextureSize();
-        if (currentBrushImage.width() > max_texture_size || currentBrushImage.height() > max_texture_size)
-            currentBrushImage = currentBrushImage.scaled(max_texture_size, max_texture_size, Qt::KeepAspectRatio);
+        QSize newSize = currentBrushImage.size();
+        newSize = newSize.boundedTo(QSize(max_texture_size, max_texture_size));
+        if (!QOpenGLContext::currentContext()->functions()->hasOpenGLFeature(QOpenGLFunctions::NPOTTextureRepeat)) {
+            if (!isPowerOfTwo(newSize.width()) || !isPowerOfTwo(newSize.height())) {
+                newSize.setHeight(qNextPowerOfTwo(newSize.height() - 1));
+                newSize.setWidth(qNextPowerOfTwo(newSize.width() - 1));
+            }
+        }
+        if (currentBrushImage.size() != newSize)
+            currentBrushImage = currentBrushImage.scaled(newSize, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
 
         GLuint wrapMode = GL_REPEAT;
-        if (QOpenGLContext::currentContext()->isOpenGLES()) {
-            // OpenGL ES does not support GL_REPEAT wrap modes for NPOT textures. So instead,
-            // we emulate GL_REPEAT by only taking the fractional part of the texture coords
-            // in the qopenglslTextureBrushSrcFragmentShader program.
-            wrapMode = GL_CLAMP_TO_EDGE;
-        }
 
         updateTexture(QT_BRUSH_TEXTURE_UNIT, currentBrushImage, wrapMode, filterMode, ForceUpdate);
     }