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120 lines
4.0 KiB
C++
120 lines
4.0 KiB
C++
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef GFX_BLUR_H
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#define GFX_BLUR_H
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#include "gfxTypes.h"
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#include "nsSize.h"
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#include "nsAutoPtr.h"
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#include "gfxPoint.h"
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class gfxContext;
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class gfxImageSurface;
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struct gfxRect;
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namespace mozilla {
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namespace gfx {
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class AlphaBoxBlur;
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}
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}
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/**
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* Implementation of a triple box blur approximation of a Gaussian blur.
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*
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* A Gaussian blur is good for blurring because, when done independently
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* in the horizontal and vertical directions, it matches the result that
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* would be obtained using a different (rotated) set of axes. A triple
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* box blur is a very close approximation of a Gaussian.
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*
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* Creates an 8-bit alpha channel context for callers to draw in,
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* spreads the contents of that context, blurs the contents, and applies
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* it as an alpha mask on a different existing context.
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*
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* A spread N makes each output pixel the maximum value of all source
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* pixels within a square of side length 2N+1 centered on the output pixel.
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*
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* A temporary surface is created in the Init function. The caller then draws
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* any desired content onto the context acquired through GetContext, and lastly
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* calls Paint to apply the blurred content as an alpha mask.
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*/
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class gfxAlphaBoxBlur
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{
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public:
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gfxAlphaBoxBlur();
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~gfxAlphaBoxBlur();
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/**
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* Constructs a box blur and initializes the temporary surface.
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* @param aRect The coordinates of the surface to create in device units.
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*
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* @param aBlurRadius The blur radius in pixels. This is the radius of
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* the entire (triple) kernel function. Each individual box blur has
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* radius approximately 1/3 this value, or diameter approximately 2/3
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* this value. This parameter should nearly always be computed using
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* CalculateBlurRadius, below.
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*
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* @param aDirtyRect A pointer to a dirty rect, measured in device units,
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* if available. This will be used for optimizing the blur operation. It
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* is safe to pass nullptr here.
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*
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* @param aSkipRect A pointer to a rect, measured in device units, that
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* represents an area where blurring is unnecessary and shouldn't be done
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* for speed reasons. It is safe to pass nullptr here.
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*/
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gfxContext* Init(const gfxRect& aRect,
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const gfxIntSize& aSpreadRadius,
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const gfxIntSize& aBlurRadius,
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const gfxRect* aDirtyRect,
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const gfxRect* aSkipRect);
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/**
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* Returns the context that should be drawn to supply the alpha mask to be
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* blurred. If the returned surface is null, then there was an error in
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* its creation.
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*/
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gfxContext* GetContext()
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{
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return mContext;
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}
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/**
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* Does the actual blurring/spreading and mask applying. Users of this
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* object must have drawn whatever they want to be blurred onto the internal
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* gfxContext returned by GetContext before calling this.
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*
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* @param aDestinationCtx The graphics context on which to apply the
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* blurred mask.
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*/
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void Paint(gfxContext* aDestinationCtx, const gfxPoint& offset = gfxPoint(0.0, 0.0));
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/**
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* Calculates a blur radius that, when used with box blur, approximates
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* a Gaussian blur with the given standard deviation. The result of
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* this function should be used as the aBlurRadius parameter to Init,
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* above.
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*/
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static gfxIntSize CalculateBlurRadius(const gfxPoint& aStandardDeviation);
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protected:
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/**
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* The context of the temporary alpha surface.
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*/
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nsRefPtr<gfxContext> mContext;
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/**
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* The temporary alpha surface.
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*/
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nsRefPtr<gfxImageSurface> mImageSurface;
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/**
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* The object that actually does the blurring for us.
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*/
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mozilla::gfx::AlphaBoxBlur *mBlur;
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};
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#endif /* GFX_BLUR_H */
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