Public Member Functions
SkV3	transform (const SkM44 &m, const SkV4 &cornerMapping, const SkV2 &cornerPt, const SkV2 &cornerRadii, const SkV4 &devCenter, float centerWeight, float strokeRadius, float joinScale, float localAARadius) const

Public Attributes
SkV2	fPosition

SkV2	fNormal

float	fStrokeScale

float	fMirrorScale

float	fCenterWeight

Detailed Description

Definition at line 107 of file GraphitePrimitivesSlide.cpp.

Member Function Documentation

◆ transform()

SkV3 LocalCornerVert::transform	(	const SkM44 &	m,
		const SkV4 &	cornerMapping,
		const SkV2 &	cornerPt,
		const SkV2 &	cornerRadii,
		const SkV4 &	devCenter,
		float	centerWeight,
		float	strokeRadius,
		float	joinScale,
		float	localAARadius
	)		const

inline

Definition at line 117 of file GraphitePrimitivesSlide.cpp.

                                                                                   {
        const bool snapToCenter = centerWeight + fCenterWeight > 0.f;
        if (snapToCenter) {
            return {devCenter.x, devCenter.y, devCenter.w};
        } else {
            // Normalized position before any additional AA offsets
            SkV2 normalizedPos = fPosition + joinScale*fMirrorScale*SkV2{fPosition.y, fPosition.x};
            // scales the normalized unit corner to the actual radii of the corner, before any AA
            // offsets are added.
            SkV2 scale = cornerRadii + SkV2{fStrokeScale*strokeRadius, fStrokeScale*strokeRadius};
            normalizedPos = scale*normalizedPos - cornerRadii;
 
            if (fStrokeScale < 0.f) {
                // An inset, which means it might cross over or might be forced to the center
                SkV2 maxInset = scale - SkV2{localAARadius, localAARadius};
                if (maxInset.x < 0.f || maxInset.y < 0.f) {
                    normalizedPos =
                            SkV2{std::min(maxInset.x, 0.f), std::min(maxInset.y, 0.f)}
                            - cornerRadii;
                } else {
                    normalizedPos += localAARadius * fNormal;
                }
            } // else no normal offsetting, or device-space offsetting
 
            SkV2 localPos =
                   {cornerMapping.x*normalizedPos.x + cornerMapping.y*normalizedPos.y + cornerPt.x,
                    cornerMapping.z*normalizedPos.x + cornerMapping.w*normalizedPos.y + cornerPt.y};
            SkV4 devPos = m.map(localPos.x, localPos.y, 0.f, 1.f);
 
            const bool deviceSpaceNormal =
                    fStrokeScale > 0.f && (fNormal.x > 0.f || fNormal.y > 0.f);
            if (deviceSpaceNormal) {
                SkV2 devNorm;
                {
                    // To calculate a device-space normal, we use the normal matrix (A^-1)^T where
                    // A is CTM * T(cornerPt) * cornerMapping * scale. We inline the calculation
                    // of (T(cornerPt)*cornerMapping*scale)^-1^T * [nx, ny, 0, 0] = N', which means
                    // that CTM^-1^T * N' is equivalent to N'^T*CTM^-1, which can be calculated with
                    // two dot products if the CTM inverse is uploaded to the GPU.
 
                    // We add epsilon so that rectangular corners are not degenerate, and circular
                    // corners remain unmodified. This only slightly increases inaccuracy for
                    // elliptical corners.
                    float sx = (scale.y + SK_ScalarNearlyZero) / (scale.x + SK_ScalarNearlyZero);
                    // Needed to calculate intermediate W of transformed normal.
                    float px = cornerMapping.y*cornerPt.y - cornerMapping.w*cornerPt.x;
                    float py = cornerMapping.z*cornerPt.x - cornerMapping.x*cornerPt.y;
                    // Inverse CTM, presumably calculated once as a uniform
                    SkM44 inv;
                    SkAssertResult(m.invert(&inv));
 
                    SkV4 normX4 = { sx*cornerMapping.w*fNormal.x,
                                   -sx*cornerMapping.y*fNormal.x,
                                   0.f,
                                   sx*px*fNormal.x};
                    SkV4 normY4 = {-cornerMapping.z*fNormal.y,
                                    cornerMapping.x*fNormal.y,
                                   0.f,
                                   py*fNormal.y};
 
                    SkV2 normX = {inv.col(0).dot(normX4), inv.col(1).dot(normX4)};
                    SkV2 normY = {inv.col(0).dot(normY4), inv.col(1).dot(normY4)};
 
                    if (joinScale == kMiterScale && fNormal.x > 0.f && fNormal.y > 0.f) {
                        // normX and normY represent adjacent edges' normals, so if we normalize
                        // them before adding together, we'll have a vector that bisects the edge
                        // normals instead of a vector matching fNormal, which is what we want when
                        // we're at a miter corner.
                        normX = normX.normalize();
                        normY = normY.normalize();
                        if (normX.dot(normY) < -0.8) {
                            // Nearly opposite directions, so the sum could have cancellation, so
                            // instead bisect orthogonal vectors and flip to keep consistent
                            float sign = normX.cross(normY) >= 0.f ? 1.f : -1.f;
                            normX = sign*SkV2{-normX.y, normX.x};
                            normY = sign*SkV2{normY.y, -normY.x};
                        }
                    }
 
                    devNorm = (normX + normY).normalize();
                }
 
                // The local coordinates for a device-space AA outset are clamped to the non-outset
                // point, which means we don't care about remaining in the same pre-homogenous
                // divide plane. This makes it very easy to determine a homogenous coordinate that
                // projects to the correct device-space position.
                devPos.x += devPos.w * kAARadius * devNorm.x;
                devPos.y += devPos.w * kAARadius * devNorm.y;
            }
 
            return SkV3{devPos.x, devPos.y, devPos.w};
        }
    }