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 *

 *   Licensed to the Apache Software Foundation (ASF) under one or more

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#pragma once

#include <vcl/virdev.hxx>

// Helper class *exclusively* for VclProcessor2D. It should only

// be used internally, see current four usages. It is used to

// render something with mask or transparence (see MaskPrimitive2D,

// UnifiedTransparencePrimitive2D and TransparencePrimitive2D) or

// as tooling for preparing pixelized output in the renderer

// (see PatternFillPrimitive2D) if that is faster.

//

// To do so, initializing this instance takes over a lot of work

// from you:

// - It initializes a 'Content' VDev which is buffered (since it had

// shown that re-allocating all the time is slower). It checks

// visibility and all usages initializing this should check for

// isVisible() after construction.

// - It pre-initializes the 'Content' VDev with blitting the content

// of the target VDev.

// - It offers to get a 'Transparence' VDev (also from the buffer) if

// needed.

//

// If 'Transparence' is/was used, it combines as needed to paint

// all buffered stuff to target VDev when calling paint().

// Caution: It is designed to use *either* a fixed transparence in

// the paint()-call *or* a fill TransparenceChannel using a

// 'Transparence' VDev. It is *not* designed to use/combine

// both - it's simply not needed for it's intended purpose/usage.

//

// Painting transparent works based on a simple principle: It first

// blits the original content of the target VDev. Then the content

// is painted on top of that, plus a Transparence/Mask prepared.

// The combination always works since unchanged pixels will not

// change, independent of the transparence value [0..255] it gets

// mixed with. Or the other way around: Only pixels changed on the

// Content *can* be changed by transparence values.

//

// This is 2.5 times faster than first painting to a

// 'combined' VDev that supports transparency, as is used by the

// presentation engine.

// For the mentioned factor refer to:

//   Patch to demonstrate former and now repaint differences

//   https://gerrit.libreoffice.org/c/core/+/129301

//   git fetch https://git.libreoffice.org/core refs/changes/01/129301/3 && git cherry-pick FETCH_HEAD

//

// Note: This principle only works when the target is RGB, so

// useful for EditViews like for PrimitiveRenderers where this is

// the case. For usage with GBA targets the starting conditions

// would have to be modified to not blend against the initial color

// of 'Content' (usually COL_WHITE).

//

// After having finished the rework of ShadowPrimitive2D,

// SoftEdgePrimitive2D and GlowPrimitive2D (see commits:)

//      e735ad1c57cddaf17d6ffc0cf15b5e14fa63c4ad

//      707b0c328a282d993fa33b618083d20b6c521de6

//      c2d1458723c66c2fd717a112f89f773226adc841

// which used the impBufferDevice in such a mode combined with

// mentioned 'combined' transparence VDev it is now possible

// to return to this former, much faster method.

//

// Please do *not* hack/use this helper class, better create

// a new one fitting your/the intended purpose. I do not want

// to see losing performance by this getting modified again.

//

// Note: Using that 'combined' transparence VDev is not really

// recommended, it may vanish anytime. That it works with

// PrimitiveRenderers *at all* is neither designed nor tested

// or recommended - it's pure coincidence.

//

// I hope that for the future all this will vanish by getting to

// fully RGBA-capable devices - what is planned and makes sense.

namespace drawinglayer

{

class impBufferDevice

{

    OutputDevice& mrOutDev;

    VclPtr<VirtualDevice> mpContent;

    VclPtr<VirtualDevice> mpAlpha;

    tools::Rectangle maDestPixel;

public:

    impBufferDevice(OutputDevice& rOutDev, const tools::Rectangle& rDestPixel);

    ~impBufferDevice();

    void paint(double fTrans = 0.0);

    bool isVisible() const { return !maDestPixel.IsEmpty(); }

    VirtualDevice& getContent();

    VirtualDevice& getTransparence();

};

} // end of namespace drawinglayer

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