1 /*
2 * Copyright 2019 Google LLC
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8 #ifndef GrQuadUtils_DEFINED
9 #define GrQuadUtils_DEFINED
10
11 #include "include/private/SkVx.h"
12 #include "src/gpu/geometry/GrQuad.h"
13
14 enum class GrQuadAAFlags;
15 enum class GrAA : bool;
16 enum class GrAAType : unsigned;
17 struct SkRect;
18
19 namespace GrQuadUtils {
20
21 // Resolve disagreements between the overall requested AA type and the per-edge quad AA flags.
22 // Both outAAType and outEdgeFlags will be updated.
23 void ResolveAAType(GrAAType requestedAAType, GrQuadAAFlags requestedEdgeFlags,
24 const GrQuad& quad, GrAAType* outAAtype, GrQuadAAFlags* outEdgeFlags);
25
26 /**
27 * Clip the device vertices of 'quad' to be in front of the W = 0 plane (w/in epsilon). The
28 * local coordinates will be updated to match the new clipped vertices. This returns the number
29 * of clipped quads that need to be drawn: 0 if 'quad' was entirely behind the plane, 1 if
30 * 'quad' did not need to be clipped or if 2 or 3 vertices were clipped, or 2 if 'quad' had one
31 * vertex clipped (producing a pentagonal shape spanned by 'quad' and 'extraVertices').
32 */
33 int ClipToW0(DrawQuad* quad, DrawQuad* extraVertices);
34
35 /**
36 * Crops quad to the provided device-space axis-aligned rectangle. If the intersection of this
37 * quad (projected) and cropRect results in a quadrilateral, this returns true. If not, this
38 * quad may be updated to be a smaller quad of the same type such that its intersection with
39 * cropRect is visually the same. This function assumes that the 'quad' coordinates are finite.
40 *
41 * The provided edge flags are updated to reflect edges clipped by cropRect (toggling on or off
42 * based on cropAA policy). If provided, the local coordinates will be updated to reflect the
43 * updated device coordinates of this quad.
44 *
45 * If 'computeLocal' is false, the local coordinates in 'quad' will not be modified.
46 */
47 bool CropToRect(const SkRect& cropRect, GrAA cropAA, DrawQuad* quad, bool computeLocal=true);
48
49 inline void Outset(const skvx::Vec<4, float>& edgeDistances, GrQuad* quad);
50
51 bool WillUseHairline(const GrQuad& quad, GrAAType aaType, GrQuadAAFlags edgeFlags);
52
53 class TessellationHelper {
54 public:
55 // Set the original device and (optional) local coordinates that are inset or outset
56 // by the requested edge distances. Use nullptr if there are no local coordinates to update.
57 // This assumes all device coordinates have been clipped to W > 0.
58 void reset(const GrQuad& deviceQuad, const GrQuad* localQuad);
59
60 // Calculates a new quadrilateral with edges parallel to the original except that they
61 // have been moved inwards by edgeDistances (which should be positive). Distances are
62 // ordered L, B, T, R to match CCW tristrip ordering of GrQuad vertices. Edges that are
63 // not moved (i.e. distance == 0) will not be used in calculations and the corners will
64 // remain on that edge.
65 //
66 // The per-vertex coverage will be returned. When the inset geometry does not collapse to
67 // a point or line, this will be 1.0 for every vertex. When it does collapse, the per-vertex
68 // coverages represent estimated pixel coverage to simulate drawing the subpixel-sized
69 // original quad.
70 //
71 // Note: the edge distances are in device pixel units, so after rendering the new quad
72 // edge's shortest distance to the original quad's edge would be equal to provided edge dist
73 skvx::Vec<4, float> inset(const skvx::Vec<4, float>& edgeDistances,
74 GrQuad* deviceInset, GrQuad* localInset);
75
76 // Calculates a new quadrilateral that outsets the original edges by the given distances.
77 // Other than moving edges outwards, this function is equivalent to inset(). If the exact
78 // same edge distances are provided, certain internal computations can be reused across
79 // consecutive calls to inset() and outset() (in any order).
80 void outset(const skvx::Vec<4, float>& edgeDistances,
81 GrQuad* deviceOutset, GrQuad* localOutset);
82
83 // Compute the edge equations of the original device space quad passed to 'reset()'. The
84 // coefficients are stored per-edge in 'a', 'b', and 'c', such that ax + by + c = 0, and
85 // a positive distance indicates the interior of the quad. Edges are ordered L, B, T, R,
86 // matching edge distances passed to inset() and outset().
87 void getEdgeEquations(skvx::Vec<4, float>* a,
88 skvx::Vec<4, float>* b,
89 skvx::Vec<4, float>* c);
90
91 // Compute the edge lengths of the original device space quad passed to 'reset()'. The
92 // edge lengths are ordered LBTR to match distances passed to inset() and outset().
93 skvx::Vec<4, float> getEdgeLengths();
94
95 // Determine if the original device space quad has vertices closer than 1px to its opposing
96 // edges, without going through the full work of computing the insets (assuming that the
97 // inset distances would be 0.5px).
98 bool isSubpixel();
99
100 private:
101 // NOTE: This struct is named 'EdgeVectors' because it holds a lot of cached calculations
102 // pertaining to the edge vectors of the input quad, projected into 2D device coordinates.
103 // While they are not direction vectors, this struct represents a convenient storage space
104 // for the projected corners of the quad.
105 struct EdgeVectors {
106 // Projected corners (x/w and y/w); these are the 2D coordinates that determine the
107 // actual edge direction vectors, dx, dy, and invLengths
108 skvx::Vec<4, float> fX2D, fY2D;
109 // Normalized edge vectors of the device space quad, ordered L, B, T, R
110 // (i.e. next_ccw(x) - x).
111 skvx::Vec<4, float> fDX, fDY;
112 // Reciprocal of edge length of the device space quad, i.e. 1 / sqrt(dx*dx + dy*dy)
113 skvx::Vec<4, float> fInvLengths;
114 // Theta represents the angle formed by the two edges connected at each corner.
115 skvx::Vec<4, float> fCosTheta;
116 skvx::Vec<4, float> fInvSinTheta; // 1 / sin(theta)
117
118 void reset(const skvx::Vec<4, float>& xs, const skvx::Vec<4, float>& ys,
119 const skvx::Vec<4, float>& ws, GrQuad::Type quadType);
120 };
121
122 struct EdgeEquations {
123 // a * x + b * y + c = 0; positive distance is inside the quad; ordered LBTR.
124 skvx::Vec<4, float> fA, fB, fC;
125
126 void reset(const EdgeVectors& edgeVectors);
127
128 skvx::Vec<4, float> estimateCoverage(const skvx::Vec<4, float>& x2d,
129 const skvx::Vec<4, float>& y2d) const;
130
131 bool isSubpixel(const skvx::Vec<4, float>& x2d, const skvx::Vec<4, float>& y2d) const;
132
133 // Outsets or insets 'x2d' and 'y2d' in place. To be used when the interior is very
134 // small, edges are near parallel, or edges are very short/zero-length. Returns number
135 // of effective vertices in the degenerate quad.
136 int computeDegenerateQuad(const skvx::Vec<4, float>& signedEdgeDistances,
137 skvx::Vec<4, float>* x2d, skvx::Vec<4, float>* y2d,
138 skvx::Vec<4, int32_t>* aaMask) const;
139 };
140
141 struct OutsetRequest {
142 // Positive edge distances to move each edge of the quad. These distances represent the
143 // shortest (perpendicular) distance between the original edge and the inset or outset
144 // edge. If the distance is 0, then the edge will not move.
145 skvx::Vec<4, float> fEdgeDistances;
146 // True if the new corners cannot be calculated by simply adding scaled edge vectors.
147 // The quad may be degenerate because of the original geometry (near colinear edges), or
148 // be because of the requested edge distances (collapse of inset, etc.)
149 bool fInsetDegenerate;
150 bool fOutsetDegenerate;
151
152 void reset(const EdgeVectors& edgeVectors, GrQuad::Type quadType,
153 const skvx::Vec<4, float>& edgeDistances);
154 };
155
156 struct Vertices {
157 // X, Y, and W coordinates in device space. If not perspective, w should be set to 1.f
158 skvx::Vec<4, float> fX, fY, fW;
159 // U, V, and R coordinates representing local quad.
160 // Ignored depending on uvrCount (0, 1, 2).
161 skvx::Vec<4, float> fU, fV, fR;
162 int fUVRCount;
163
164 void reset(const GrQuad& deviceQuad, const GrQuad* localQuad);
165
166 void asGrQuads(GrQuad* deviceOut, GrQuad::Type deviceType,
167 GrQuad* localOut, GrQuad::Type localType) const;
168
169 // Update the device and optional local coordinates by moving the corners along their
170 // edge vectors such that the new edges have moved 'signedEdgeDistances' from their
171 // original lines. This should only be called if the 'edgeVectors' fInvSinTheta data is
172 // numerically sound.
173 void moveAlong(const EdgeVectors& edgeVectors,
174 const skvx::Vec<4, float>& signedEdgeDistances);
175
176 // Update the device coordinates by deriving (x,y,w) that project to (x2d, y2d), with
177 // optional local coordinates updated to match the new vertices. It is assumed that
178 // 'mask' was respected when determining (x2d, y2d), but it is used to ensure that only
179 // unmasked unprojected edge vectors are used when computing device and local coords.
180 void moveTo(const skvx::Vec<4, float>& x2d,
181 const skvx::Vec<4, float>& y2d,
182 const skvx::Vec<4, int32_t>& mask);
183 };
184
185 Vertices fOriginal;
186 EdgeVectors fEdgeVectors;
187 GrQuad::Type fDeviceType;
188 GrQuad::Type fLocalType;
189
190 // Lazily computed as needed; use accessor functions instead of direct access.
191 OutsetRequest fOutsetRequest;
192 EdgeEquations fEdgeEquations;
193
194 // Validity of Vertices/EdgeVectors (always true after first call to set()).
195 bool fVerticesValid = false;
196 // Validity of outset request (true after calling getOutsetRequest() until next set() call
197 // or next inset/outset() with different edge distances).
198 bool fOutsetRequestValid = false;
199 // Validity of edge equations (true after calling getEdgeEquations() until next set() call).
200 bool fEdgeEquationsValid = false;
201
202 // The requested edge distances must be positive so that they can be reused between inset
203 // and outset calls.
204 const OutsetRequest& getOutsetRequest(const skvx::Vec<4, float>& edgeDistances);
205 const EdgeEquations& getEdgeEquations();
206
207 // Outsets or insets 'vertices' by the given perpendicular 'signedEdgeDistances' (inset or
208 // outset is determined implicitly by the sign of the distances).
209 void adjustVertices(const skvx::Vec<4, float>& signedEdgeDistances, Vertices* vertices);
210 // Like adjustVertices() but handles empty edges, collapsed quads, numerical issues, and
211 // returns the number of effective vertices in the adjusted shape.
212 int adjustDegenerateVertices(const skvx::Vec<4, float>& signedEdgeDistances,
213 Vertices* vertices);
214
215 friend int ClipToW0(DrawQuad*, DrawQuad*); // To reuse Vertices struct
216 };
217
218 }; // namespace GrQuadUtils
219
Outset(const skvx::Vec<4,float> & edgeDistances,GrQuad * quad)220 void GrQuadUtils::Outset(const skvx::Vec<4, float>& edgeDistances, GrQuad* quad) {
221 TessellationHelper outsetter;
222 outsetter.reset(*quad, nullptr);
223 outsetter.outset(edgeDistances, quad, nullptr);
224 }
225
226 #endif
227