diff options
Diffstat (limited to 'src/effects/SkBlurMask.cpp')
| -rw-r--r-- | src/effects/SkBlurMask.cpp | 162 |
1 files changed, 161 insertions, 1 deletions
diff --git a/src/effects/SkBlurMask.cpp b/src/effects/SkBlurMask.cpp index 658b0fd47e..766da539fe 100644 --- a/src/effects/SkBlurMask.cpp +++ b/src/effects/SkBlurMask.cpp @@ -12,6 +12,14 @@ #include "SkTemplates.h" #include "SkEndian.h" +// scale factor for the blur radius to match the behavior of the all existing blur +// code (both on the CPU and the GPU). This magic constant is 1/sqrt(3). + +// TODO: get rid of this fudge factor and move any required fudging up into +// the calling library + +#define kBlurRadiusFudgeFactor SkFloatToScalar( .57735f ) + #define UNROLL_SEPARABLE_LOOPS /** @@ -866,7 +874,7 @@ bool SkBlurMask::Blur(SkMask* dst, const SkMask& src, // highQuality: use three box blur passes as a cheap way to approximate a Gaussian blur int passCount = (kHigh_Quality == quality) ? 3 : 1; - SkScalar passRadius = SkScalarDiv(radius, SkScalarSqrt(SkIntToScalar(passCount))); + SkScalar passRadius = (kHigh_Quality == quality) ? SkScalarMul( radius, kBlurRadiusFudgeFactor): radius; int rx = SkScalarCeil(passRadius); int outer_weight = 255 - SkScalarRound((SkIntToScalar(rx) - passRadius) * 255); @@ -1021,3 +1029,155 @@ bool SkBlurMask::Blur(SkMask* dst, const SkMask& src, { return SkBlurMask::Blur(dst, src, radius, style, quality, margin, false); } + +/* Convolving a box with itself three times results in a piecewise + quadratic function: + + 0 x <= -1.5 + 9/8 + 3/2 x + 1/2 x^2 -1.5 < x <= 1.5 + 3/4 - x^2 -.5 < x <= .5 + 9/8 - 3/2 x + 1/2 x^2 0.5 < x <= 1.5 + 0 1.5 < x + + To get the profile curve of the blurred step function at the rectangle + edge, we evaluate the indefinite integral, which is piecewise cubic: + + 0 x <= -1.5 + 5/8 + 9/8 x + 3/4 x^2 + 1/6 x^3 -1.5 < x <= -0.5 + 1/2 + 3/4 x - 1/3 x^3 -.5 < x <= .5 + 3/8 + 9/8 x - 3/4 x^2 + 1/6 x^3 .5 < x <= 1.5 + 1 1.5 < x +*/ + +static float gaussian_integral( float x ) { + if ( x > 1.5f ) { + return 0.0f; + } + if ( x < -1.5f ) { + return 1.0f; + } + + float x2 = x*x; + float x3 = x2*x; + + if ( x > 0.5 ) { + return .5625 - ( x3 / 6 - 3 * x2 / 4 + 1.125 * x); + } + if ( x > -0.5 ) { + return 0.5 - (0.75 * x - x3 / 3); + } + return 0.4375 + (-x3 / 6 - 3 * x2 / 4 - 1.125 * x); +} + +/* + compute_profile allocates and fills in an array of floating + point values between 0 and 255 for the profile signature of + a blurred half-plane with the given blur radius. Since we're + going to be doing screened multiplications (i.e., 1 - (1-x)(1-y)) + all the time, we actually fill in the profile pre-inverted + (already done 255-x). + + The function returns the size of the array allocated for the + profile. It's the responsibility of the caller to delete the + memory returned in profile_out. +*/ + +static int compute_profile( SkScalar radius, unsigned int **profile_out ) { + int size = radius * 3 + 1; + int center = size >> 1; + + unsigned int *profile = new unsigned int [size]; + + float invr = 1.0f/radius; + + profile[0] = 255; + for (int x = 1 ; x < size ; x++) { + float scaled_x = ( center - x ) * invr; + float gi = gaussian_integral( scaled_x ); + profile[x] = 255 - (uint8_t) ( 255.f * gi ); + } + + *profile_out = profile; + return size; +} + +// TODO MAYBE: Maintain a profile cache to avoid recomputing this for +// commonly used radii. Consider baking some of the most common blur radii +// directly in as static data? + +// Implementation adapted from Michael Herf's approach: +// http://stereopsis.com/shadowrect/ + +bool SkBlurMask::BlurRect(SkMask *dst, const SkRect &src, + SkScalar provided_radius, Style style, Quality quality, + SkIPoint *margin) { + int profile_size; + unsigned int *profile; + + + float radius = SkScalarToFloat( SkScalarMul( provided_radius, kBlurRadiusFudgeFactor ) ); + + profile_size = compute_profile( radius, &profile ); + + int pad = (int) (radius * 1.5f + 1); + if (margin) { + margin->set( pad, pad ); + } + dst->fBounds = SkIRect::MakeWH(src.width(), src.height()); + dst->fBounds.outset(pad, pad); + + dst->fRowBytes = dst->fBounds.width(); + dst->fFormat = SkMask::kA8_Format; + dst->fImage = NULL; + + size_t dstSize = dst->computeImageSize(); + if (0 == dstSize) { + return false; // too big to allocate, abort + } + + int sw = src.width(); + int sh = src.height(); + + uint8_t* dp = SkMask::AllocImage(dstSize); + + dst->fImage = dp; + + SkAutoTCallVProc<uint8_t, SkMask_FreeImage> autoCall(dp); + + int dst_height = dst->fBounds.height(); + int dst_width = dst->fBounds.width(); + + // nearest odd number less than the profile size represents the center + // of the (2x scaled) profile + int center = ( profile_size & ~1 ) - 1; + + int w = sw - center; + int h = sh - center; + + uint8_t *outptr = dp; + + for (int y = 0 ; y < dst_height ; y++) + { + // time to fill in a scanline of the blurry rectangle. + // to avoid floating point math, everything is multiplied by + // 2 where needed. This keeps things nice and integer-oriented. + + int dy = abs((y << 1) - dst_height) - h; // how far are we from the original edge? + int oy = dy >> 1; + if (oy < 0) oy = 0; + + unsigned int profile_y = profile[oy]; + + for (int x = 0 ; x < (dst_width << 1) ; x += 2) { + int dx = abs( x - dst_width ) - w; + int ox = dx >> 1; + if (ox < 0) ox = 0; + + unsigned int maskval = SkMulDiv255Round(profile[ox], profile_y); + + *(outptr++) = maskval; + } + } + + return true; +} |