[PATCH] Forward-port surface dithering from CM10.2

0001-Forward-port-surface-dithering-from-CM10.2.patch

From f6cceade46953f40fa9eca9d737dbcd0da7b969b Mon Sep 17 00:00:00 2001
From: Steven Luo <steven@steven676.net>
Date: Sat, 30 Mar 2013 00:44:11 -0700
Subject: [PATCH] Forward-port surface dithering from CM10.2

This allows the use of 16-bit color displays without excessive color
banding;

Change-Id: Icb469b9cb4beb686516c60bb576dbd0a73f505e0
---
 include/ui/PixelFormat.h                              |    1 +
 libs/ui/PixelFormat.cpp                               |   16 ++++++++++++++++
 services/surfaceflinger/Layer.cpp                     |    9 +++++++++
 services/surfaceflinger/Layer.h                       |    6 ++++++
 services/surfaceflinger/RenderEngine/RenderEngine.cpp |    8 ++++++++
 services/surfaceflinger/RenderEngine/RenderEngine.h   |    2 ++
 services/surfaceflinger/SurfaceFlinger.cpp            |    9 ++++++++-
 services/surfaceflinger/SurfaceFlinger.h              |    6 ++++++
 8 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/include/ui/PixelFormat.h b/include/ui/PixelFormat.h
index 19228c4..6278d7a 100644
--- a/include/ui/PixelFormat.h
+++ b/include/ui/PixelFormat.h
@@ -122,6 +122,7 @@ status_t getPixelFormatInfo(PixelFormat format, PixelFormatInfo* info);
 
 ssize_t bytesPerPixel(PixelFormat format);
 ssize_t bitsPerPixel(PixelFormat format);
+ssize_t minColorDepth(PixelFormat format);
 
 }; // namespace android
 
diff --git a/libs/ui/PixelFormat.cpp b/libs/ui/PixelFormat.cpp
index 0595315..e82f309 100644
--- a/libs/ui/PixelFormat.cpp
+++ b/libs/ui/PixelFormat.cpp
@@ -160,6 +160,22 @@ ssize_t bitsPerPixel(PixelFormat format) {
     return BAD_VALUE;
 }
 
+ssize_t minColorDepth(PixelFormat format) {
+    switch (format) {
+        case PIXEL_FORMAT_RGBA_8888:
+        case PIXEL_FORMAT_RGBX_8888:
+        case PIXEL_FORMAT_BGRA_8888:
+        case PIXEL_FORMAT_RGB_888:
+            return 8;
+        case PIXEL_FORMAT_RGB_565:
+        case PIXEL_FORMAT_RGBA_5551:
+            return 5;
+        case PIXEL_FORMAT_RGBA_4444:
+            return 4;
+    }
+    return BAD_VALUE;
+}
+
 // ----------------------------------------------------------------------------
 }; // namespace android
 // ----------------------------------------------------------------------------
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index dd66f0b..0b668f6 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -68,6 +68,7 @@ Layer::Layer(SurfaceFlinger* flinger, const sp<Client>& client,
         mDebug(false),
         mFormat(PIXEL_FORMAT_NONE),
         mOpaqueLayer(true),
+        mNeedsDithering(false),
         mTransactionFlags(0),
         mQueuedFrames(0),
         mCurrentTransform(0),
@@ -199,6 +200,12 @@ status_t Layer::setBuffers( uint32_t w, uint32_t h,
     mSurfaceFlingerConsumer->setDefaultBufferFormat(format);
     mSurfaceFlingerConsumer->setConsumerUsageBits(getEffectiveUsage(0));
 
+    if (mFlinger->getUseDithering()) {
+        int displayMinColorDepth = mFlinger->getMinColorDepth();
+        int layerMinColorDepth = minColorDepth(format);
+        mNeedsDithering = (layerMinColorDepth > displayMinColorDepth);
+    }
+
     return NO_ERROR;
 }
 
@@ -573,6 +580,7 @@ void Layer::clearWithOpenGL(const sp<const DisplayDevice>& hw, const Region& cli
 {
     RenderEngine& engine(mFlinger->getRenderEngine());
     computeGeometry(hw, mMesh);
+    engine.setDither(false);
     engine.setupFillWithColor(red, green, blue, alpha);
     engine.drawMesh(mMesh);
 }
@@ -619,6 +627,7 @@ void Layer::drawWithOpenGL(
     texCoords[3] = vec2(right, 1.0f - top);
 
     RenderEngine& engine(mFlinger->getRenderEngine());
+    engine.setDither(needsDithering());
     engine.setupLayerBlending(mPremultipliedAlpha, isOpaque(), s.alpha);
     engine.drawMesh(mMesh);
     engine.disableBlending();
diff --git a/services/surfaceflinger/Layer.h b/services/surfaceflinger/Layer.h
index 9c36349..807d6af 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -153,6 +153,11 @@ public:
     virtual bool isOpaque() const;
 
     /*
+     * needsDithering - true if this surface needs dithering
+     */
+    virtual bool needsDithering() const     { return mNeedsDithering; }
+
+    /*
      * isSecure - true if this surface is secure, that is if it prevents
      * screenshots or VNC servers.
      */
@@ -340,6 +345,7 @@ private:
     mutable bool mDebug;
     PixelFormat mFormat;
     bool mOpaqueLayer;
+    bool mNeedsDithering;
 
     // these are protected by an external lock
     State mCurrentState;
diff --git a/services/surfaceflinger/RenderEngine/RenderEngine.cpp b/services/surfaceflinger/RenderEngine/RenderEngine.cpp
index 53aa85b..56d261a 100644
--- a/services/surfaceflinger/RenderEngine/RenderEngine.cpp
+++ b/services/surfaceflinger/RenderEngine/RenderEngine.cpp
@@ -223,6 +223,14 @@ void RenderEngine::readPixels(size_t l, size_t b, size_t w, size_t h, uint32_t*
     glReadPixels(l, b, w, h, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
 }
 
+void RenderEngine::setDither(bool dither) {
+    if (dither) {
+        glEnable(GL_DITHER);
+    } else {
+        glDisable(GL_DITHER);
+    }
+}
+
 void RenderEngine::dump(String8& result) {
     const GLExtensions& extensions(GLExtensions::getInstance());
     result.appendFormat("GLES: %s, %s, %s\n",
diff --git a/services/surfaceflinger/RenderEngine/RenderEngine.h b/services/surfaceflinger/RenderEngine/RenderEngine.h
index 4ff83c0..ac4b1dc 100644
--- a/services/surfaceflinger/RenderEngine/RenderEngine.h
+++ b/services/surfaceflinger/RenderEngine/RenderEngine.h
@@ -76,6 +76,8 @@ public:
     void deleteTextures(size_t count, uint32_t const* names);
     void readPixels(size_t l, size_t b, size_t w, size_t h, uint32_t* pixels);
 
+    void setDither(bool dither);
+
     class BindImageAsFramebuffer {
         RenderEngine& mEngine;
         uint32_t mTexName, mFbName;
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 88ad0bb..385df2b 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -156,7 +156,8 @@ SurfaceFlinger::SurfaceFlinger()
         mBootFinished(false),
         mPrimaryHWVsyncEnabled(false),
         mHWVsyncAvailable(false),
-        mDaltonize(false)
+        mDaltonize(false),
+        mUseDithering(0)
 {
     ALOGI("SurfaceFlinger is starting");
 
@@ -614,6 +615,9 @@ void SurfaceFlinger::init() {
     ALOGI("Client API: %s", eglQueryString(mEGLDisplay, EGL_CLIENT_APIS)?:"Not Supported");
     ALOGI("EGLSurface: %d-%d-%d-%d, config=%p", r, g, b, a, mEGLConfig);
 
+    // assume red has minimum color depth
+    mMinColorDepth = r;
+
     // get a RenderEngine for the given display / config (can't fail)
     mRenderEngine = RenderEngine::create(mEGLDisplay, mEGLConfig);
 
@@ -651,6 +655,9 @@ void SurfaceFlinger::init() {
                 hw->acquireScreen();
             }
             mDisplays.add(token, hw);
+            if (!mUseDithering && bitsPerPixel(mHwc->getFormat(i)) <= 16) {
+                mUseDithering = 1;
+            }
         }
     }
 
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 12b07ef..0fbfcf3 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -334,6 +334,10 @@ private:
     size_t getMaxTextureSize() const;
     size_t getMaxViewportDims() const;
 
+    uint32_t getMinColorDepth() const { return mMinColorDepth; }
+    // 0: surface doesn't need dithering, 1: use if necessary
+    inline int getUseDithering() const { return mUseDithering; }
+
     /* ------------------------------------------------------------------------
      * Display and layer stack management
      */
@@ -440,6 +444,7 @@ private:
     sp<EventThread> mEventThread;
     sp<EventThread> mSFEventThread;
     sp<EventControlThread> mEventControlThread;
+    uint32_t mMinColorDepth;
     EGLContext mEGLContext;
     EGLConfig mEGLConfig;
     EGLDisplay mEGLDisplay;
@@ -467,6 +472,7 @@ private:
     volatile nsecs_t mDebugInTransaction;
     nsecs_t mLastTransactionTime;
     bool mBootFinished;
+    int mUseDithering;
 
     // these are thread safe
     mutable MessageQueue mEventQueue;
-- 
1.7.10.4