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
14enum class GrQuadAAFlags;
15enum class GrAA : bool;
16enum class GrAAType : unsigned;
17struct SkRect;
18
19namespace 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
220void 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