[effects/blur] Update blur to be more natural

Summary:
This gets rid of the dark area that may appear between very different colors by doing the blur in SRGB colorspace.
This is not enabled for GLES, and will use the previous blur type.

Test Plan:
Before:
{F6577457}

After:
{F6577458}

Reviewers: #vdg, #kwin, davidedmundson, zzag, fredrik, ngraham

Reviewed By: #vdg, fredrik, ngraham

Subscribers: Codezela, fredrik, abetts, Petross404, rapiteanu, filipf, rooty, ngraham, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D18377

effects/blur/blur.cpp

@@ -126,8 +126,10 @@ void BlurEffect::updateTexture()
     m_renderTargets.reserve(m_downSampleIterations + 2);
     m_renderTextures.reserve(m_downSampleIterations + 2);
 
+    const GLenum textureFormat = GLPlatform::instance()->isGLES() ? GL_RGBA8 : GL_SRGB8_ALPHA8;
+
     for (int i = 0; i <= m_downSampleIterations; i++) {
-        m_renderTextures.append(GLTexture(GL_RGBA8, effects->virtualScreenSize() / (1 << i)));
+        m_renderTextures.append(GLTexture(textureFormat, effects->virtualScreenSize() / (1 << i)));
         m_renderTextures.last().setFilter(GL_LINEAR);
         m_renderTextures.last().setWrapMode(GL_CLAMP_TO_EDGE);
 
@@ -135,7 +137,7 @@ void BlurEffect::updateTexture()
     }
 
     // This last set is used as a temporary helper texture
-    m_renderTextures.append(GLTexture(GL_RGBA8, effects->virtualScreenSize()));
+    m_renderTextures.append(GLTexture(textureFormat, effects->virtualScreenSize()));
     m_renderTextures.last().setFilter(GL_LINEAR);
     m_renderTextures.last().setWrapMode(GL_CLAMP_TO_EDGE);
 
@@ -641,6 +643,8 @@ void BlurEffect::doBlur(const QRegion& shape, const QRect& screen, const float o
 
     const QRegion expandedBlurRegion = expand(shape) & expand(screen);
 
+    const bool isGLES = GLPlatform::instance()->isGLES();
+
     // Upload geometry for the down and upsample iterations
     GLVertexBuffer *vbo = GLVertexBuffer::streamingBuffer();
 
@@ -662,10 +666,19 @@ void BlurEffect::doBlur(const QRegion& shape, const QRect& screen, const float o
      */
     if (isDock) {
         m_renderTargets.last()->blitFromFramebuffer(sourceRect, destRect);
+
+        if (!isGLES) {
+            glEnable(GL_FRAMEBUFFER_SRGB);
+        }
+
         copyScreenSampleTexture(vbo, blurRectCount, shape.translated(xTranslate, yTranslate), screenProjection);
     } else {
         m_renderTargets.first()->blitFromFramebuffer(sourceRect, destRect);
 
+        if (!isGLES) {
+            glEnable(GL_FRAMEBUFFER_SRGB);
+        }
+
         // Remove the m_renderTargets[0] from the top of the stack that we will not use
         GLRenderTarget::popRenderTarget();
     }
@@ -689,6 +702,10 @@ void BlurEffect::doBlur(const QRegion& shape, const QRect& screen, const float o
 
     upscaleRenderToScreen(vbo, blurRectCount * (m_downSampleIterations + 1), shape.rectCount() * 6, screenProjection, windowRect.topLeft());
 
+    if (!isGLES) {
+        glDisable(GL_FRAMEBUFFER_SRGB);
+    }
+
     if (opacity < 1.0) {
         glDisable(GL_BLEND);
     }