Forward-port surface dithering from CM10

This allows the use of 16-bit color displays without excessive color
banding; behavior can be controlled by the persist.sys.use_dithering
property.

Incorporates http://review.cyanogenmod.org/19532 from CM10 as well as
code removed in upstream commit 1b03149.

Change-Id: I290ca4ed4787dc81ac756d9af92cd6a690865a08

5 files changed, 52 insertions, 2 deletions

diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 7edbdc5..c1561b2 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -63,6 +63,7 @@ Layer::Layer(SurfaceFlinger* flinger, const sp<Client>& client)
         mFormat(PIXEL_FORMAT_NONE),
         mGLExtensions(GLExtensions::getInstance()),
         mOpaqueLayer(true),
+        mNeedsDithering(false),
         mSecure(false),
         mProtectedByApp(false)
 {
@@ -194,6 +195,23 @@ status_t Layer::setBuffers( uint32_t w, uint32_t h,
     mSurfaceTexture->setDefaultBufferFormat(format);
     mSurfaceTexture->setConsumerUsageBits(getEffectiveUsage(0));
 
+    int displayMinColorDepth;
+    int layerRedsize;
+    switch (mFlinger->getUseDithering()) {
+    case 0:
+        mNeedsDithering = false;
+        break;
+    case 1:
+        displayMinColorDepth = mFlinger->getMinColorDepth();
+        // we use the red index
+        layerRedsize = info.getSize(PixelFormatInfo::INDEX_RED);
+        mNeedsDithering = (layerRedsize > displayMinColorDepth);
+        break;
+    case 2:
+        mNeedsDithering = true;
+        break;
+    }
+
     return NO_ERROR;
 }
 
diff --git a/services/surfaceflinger/Layer.h b/services/surfaceflinger/Layer.h
index c5eb26b..a3d6ab9 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -77,6 +77,7 @@ public:
     virtual uint32_t doTransaction(uint32_t transactionFlags);
     virtual Region latchBuffer(bool& recomputeVisibleRegions);
     virtual bool isOpaque() const;
+    virtual bool needsDithering() const     { return mNeedsDithering; }
     virtual bool isSecure() const           { return mSecure; }
     virtual bool isProtected() const;
     virtual void onRemoved();
@@ -142,6 +143,7 @@ private:
     PixelFormat mFormat;
     const GLExtensions& mGLExtensions;
     bool mOpaqueLayer;
+    bool mNeedsDithering;
 
     // page-flip thread (currently main thread)
     bool mSecure;         // no screenshots
diff --git a/services/surfaceflinger/LayerBase.cpp b/services/surfaceflinger/LayerBase.cpp
index 9b03c74..612e47b 100644
--- a/services/surfaceflinger/LayerBase.cpp
+++ b/services/surfaceflinger/LayerBase.cpp
@@ -354,6 +354,7 @@ void LayerBase::clearWithOpenGL(const sp<const DisplayDevice>& hw, const Region&
     glDisable(GL_TEXTURE_EXTERNAL_OES);
     glDisable(GL_TEXTURE_2D);
     glDisable(GL_BLEND);
+    glDisable(GL_DITHER);
 
     LayerMesh mesh;
     computeGeometry(hw, &mesh);
@@ -428,6 +429,12 @@ void LayerBase::drawWithOpenGL(const sp<const DisplayDevice>& hw, const Region&
         texCoords[i].v = 1.0f - texCoords[i].v;
     }
 
+    if (needsDithering()) {
+        glEnable(GL_DITHER);
+    } else {
+        glDisable(GL_DITHER);
+    }
+
     glEnableClientState(GL_TEXTURE_COORD_ARRAY);
     glTexCoordPointer(2, GL_FLOAT, 0, texCoords);
     glVertexPointer(2, GL_FLOAT, 0, mesh.getVertices());
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index dc562f1..1842949 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -104,7 +104,8 @@ SurfaceFlinger::SurfaceFlinger()
         mLastSwapBufferTime(0),
         mDebugInTransaction(0),
         mLastTransactionTime(0),
-        mBootFinished(false)
+        mBootFinished(false),
+        mUseDithering(0)
 {
     ALOGI("SurfaceFlinger is starting");
 
@@ -122,8 +123,13 @@ SurfaceFlinger::SurfaceFlinger()
             mDebugDDMS = 0;
         }
     }
+
+    property_get("persist.sys.use_dithering", value, "1");
+    mUseDithering = atoi(value);
+
     ALOGI_IF(mDebugRegion, "showupdates enabled");
     ALOGI_IF(mDebugDDMS, "DDMS debugging enabled");
+    ALOGI_IF(mUseDithering, "use dithering");
 
 #ifdef SAMSUNG_HDMI_SUPPORT
     ALOGD(">>> Run service");
@@ -429,7 +435,11 @@ void SurfaceFlinger::initializeGL(EGLDisplay display) {
     glPixelStorei(GL_PACK_ALIGNMENT, 4);
     glEnableClientState(GL_VERTEX_ARRAY);
     glShadeModel(GL_FLAT);
-    glDisable(GL_DITHER);
+    if (mUseDithering == 2) {
+        glEnable(GL_DITHER);
+    } else {
+        glDisable(GL_DITHER);
+    }
     glDisable(GL_CULL_FACE);
 
     struct pack565 {
@@ -467,6 +477,9 @@ void SurfaceFlinger::initializeGL(EGLDisplay display) {
     ALOGI("extensions: %s", extensions.getExtension());
     ALOGI("GL_MAX_TEXTURE_SIZE = %d", mMaxTextureSize);
     ALOGI("GL_MAX_VIEWPORT_DIMS = %d x %d", mMaxViewportDims[0], mMaxViewportDims[1]);
+
+    // XXX Assume bit depth for red is equal to minimum depth of all colors
+    mMinColorDepth = r;
 }
 
 status_t SurfaceFlinger::readyToRun()
@@ -564,6 +577,10 @@ uint32_t SurfaceFlinger::getMaxTextureSize() const {
     return mMaxTextureSize;
 }
 
+uint32_t SurfaceFlinger::getMinColorDepth() const {
+    return mMinColorDepth;
+}
+
 uint32_t SurfaceFlinger::getMaxViewportDims() const {
     return mMaxViewportDims[0] < mMaxViewportDims[1] ?
             mMaxViewportDims[0] : mMaxViewportDims[1];
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index e8c4b9c..050d10f 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -324,8 +324,12 @@ private:
     static EGLContext createGLContext(EGLDisplay disp, EGLConfig config);
     void initializeGL(EGLDisplay display);
     uint32_t getMaxTextureSize() const;
+    uint32_t getMinColorDepth() const;
     uint32_t getMaxViewportDims() const;
 
+    // 0: surface doesn't need dithering, 1: use if necessary, 2: use permanently
+    inline int getUseDithering() const { return mUseDithering; }
+
     /* ------------------------------------------------------------------------
      * Display and layer stack management
      */
@@ -423,6 +427,7 @@ private:
     sp<EventThread> mEventThread;
     GLint mMaxViewportDims[2];
     GLint mMaxTextureSize;
+    GLint mMinColorDepth;
     EGLContext mEGLContext;
     EGLConfig mEGLConfig;
     EGLDisplay mEGLDisplay;
@@ -448,6 +453,7 @@ private:
     volatile nsecs_t mDebugInTransaction;
     nsecs_t mLastTransactionTime;
     bool mBootFinished;
+    int mUseDithering;
 
     // these are thread safe
     mutable MessageQueue mEventQueue;