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Commit e47aadd9 authored by Chris Craik's avatar Chris Craik
Browse files

Fix blending behavior with first draw op 

Bug: 65077146
Test: Manual - uirendering tests don't allow test draw content
to be displayed first.

It's not always valid to disable blending on the first draw to the framebuffer,
since some blend modes affect the framebuffer in different ways. We now only
disable blending if the op is SRC_OVER to be safe.

For example:

    canvas.drawColor(0xfeff0000, PorterDuff.Mode.CLEAR);
    canvas.drawColor(Color.BLUE, PorterDuff.Mode.DST_OVER);

The BLUE should always be seen - the other draw should just clear the buffer.
Prior to this fix, the above code (put in a window background) would draw black.

In addition, this removes the disable behavior in drawRects(), since that should
never benefit from the optimization - that decoration is always drawn at the end
of a frame.

Change-Id: I34e8d9d62d6e1dfa00e9301f44c277475f2940a8
parent 530a2b44

libs/hwui/BakedOpRenderer.cpp

+9 −6
Original line number Diff line number Diff line
@@ -216,10 +216,7 @@ void BakedOpRenderer::drawRects(const float* rects, int count, const SkPaint* pa 
            .setTransform(Matrix4::identity(), TransformFlags::None)

            .setModelViewIdentityEmptyBounds()

            .build();

    // Disable blending if this is the first draw to the main framebuffer, in case app has defined

    // transparency where it doesn't make sense - as first draw in opaque window.

    bool overrideDisableBlending = !mHasDrawn && mOpaque && !mRenderTarget.frameBufferId;

    mRenderState.render(glop, mRenderTarget.orthoMatrix, overrideDisableBlending);

    mRenderState.render(glop, mRenderTarget.orthoMatrix, false);

    mHasDrawn = true;

}
@@ -350,8 +347,14 @@ void BakedOpRenderer::renderGlopImpl(const Rect* dirtyBounds, const ClipBase* cl 
        const Glop& glop) {

    prepareRender(dirtyBounds, clip);

    // Disable blending if this is the first draw to the main framebuffer, in case app has defined

    // transparency where it doesn't make sense - as first draw in opaque window.

    bool overrideDisableBlending = !mHasDrawn && mOpaque && !mRenderTarget.frameBufferId;

    // transparency where it doesn't make sense - as first draw in opaque window. Note that we only

    // apply this improvement when the blend mode is SRC_OVER - other modes (e.g. CLEAR) can be

    // valid draws that affect other content (e.g. draw CLEAR, then draw DST_OVER)

    bool overrideDisableBlending = !mHasDrawn

        && mOpaque

        && !mRenderTarget.frameBufferId

        && glop.blend.src == GL_ONE

        && glop.blend.dst == GL_ONE_MINUS_SRC_ALPHA;

    mRenderState.render(glop, mRenderTarget.orthoMatrix, overrideDisableBlending);

    if (!mRenderTarget.frameBufferId) mHasDrawn = true;

}