new scanconversion technique

This technique geometrically clips all segments against the clip bounds,
ensuring that we never send a value to the edgelist that might overflow in
fixedpoint.

Current disabled in SkScan_Path.cpp by a #define. There are a few minor pixel
differences between this and the old technique, as found by the gm tool, so
at the moment this new code is off by default.



git-svn-id: http://skia.googlecode.com/svn/trunk@432 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 508 insertions, 0 deletions

diff --git a/src/core/SkEdgeClipper.cpp b/src/core/SkEdgeClipper.cpp
new file mode 100644
index 0000000000..7ad845d020
--- /dev/null
+++ b/src/core/SkEdgeClipper.cpp
@@ -0,0 +1,508 @@
+/*
+ * Copyright (C) 2009 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "SkEdgeClipper.h"
+#include "SkGeometry.h"
+
+static bool quick_reject(const SkRect& bounds, const SkRect& clip) {
+    return bounds.fTop >= clip.fBottom || bounds.fBottom <= clip.fTop;
+}
+
+static inline void clamp_le(SkScalar& value, SkScalar max) {
+    if (value > max) {
+        value = max;
+    }
+}
+
+static inline void clamp_ge(SkScalar& value, SkScalar min) {
+    if (value < min) {
+        value = min;
+    }
+}
+
+/*  src[] must be monotonic in Y. This routine copies src into dst, and sorts
+ it to be increasing in Y. If it had to reverse the order of the points,
+ it returns true, otherwise it returns false
+ */
+static bool sort_increasing_Y(SkPoint dst[], const SkPoint src[], int count) {
+    // we need the data to be monotonically increasing in Y
+    if (src[0].fY > src[count - 1].fY) {
+        for (int i = 0; i < count; i++) {
+            dst[i] = src[count - i - 1];
+        }
+        return true;
+    } else {
+        memcpy(dst, src, count * sizeof(SkPoint));
+        return false;
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+static bool chopMonoQuadAt(SkScalar c0, SkScalar c1, SkScalar c2,
+                           SkScalar target, SkScalar* t) {
+    /* Solve F(t) = y where F(t) := [0](1-t)^2 + 2[1]t(1-t) + [2]t^2
+     *  We solve for t, using quadratic equation, hence we have to rearrange
+     * our cooefficents to look like At^2 + Bt + C
+     */
+    SkScalar A = c0 - c1 - c1 + c2;
+    SkScalar B = 2*(c1 - c0);
+    SkScalar C = c0 - target;
+    
+    SkScalar roots[2];  // we only expect one, but make room for 2 for safety
+    int count = SkFindUnitQuadRoots(A, B, C, roots);
+    if (count) {
+        *t = roots[0];
+        return true;
+    }
+    return false;
+}
+
+static bool chopMonoQuadAtY(SkPoint pts[3], SkScalar y, SkScalar* t) {
+    return chopMonoQuadAt(pts[0].fY, pts[1].fY, pts[2].fY, y, t);
+}
+
+static bool chopMonoQuadAtX(SkPoint pts[3], SkScalar x, SkScalar* t) {
+    return chopMonoQuadAt(pts[0].fX, pts[1].fX, pts[2].fX, x, t);
+}
+
+// Modify pts[] in place so that it is clipped in Y to the clip rect
+static void chop_quad_in_Y(SkPoint pts[3], const SkRect& clip) {
+    SkScalar t;
+    SkPoint tmp[5]; // for SkChopQuadAt
+
+    // are we partially above
+    if (pts[0].fY < clip.fTop) {
+        if (chopMonoQuadAtY(pts, clip.fTop, &t)) {
+            // take the 2nd chopped quad
+            SkChopQuadAt(pts, tmp, t);
+            clamp_ge(tmp[2].fY, clip.fTop);
+            clamp_ge(tmp[3].fY, clip.fTop);
+            pts[0] = tmp[2];
+            pts[1] = tmp[3];
+        } else {
+            // if chopMonoQuadAtY failed, then we may have hit inexact numerics
+            // so we just clamp against the top
+            for (int i = 0; i < 3; i++) {
+                if (pts[i].fY < clip.fTop) {
+                    pts[i].fY = clip.fTop;
+                }
+            }
+        }
+    }
+    
+    // are we partially below
+    if (pts[2].fY > clip.fBottom) {
+        if (chopMonoQuadAtY(pts, clip.fBottom, &t)) {
+            SkChopQuadAt(pts, tmp, t);
+            clamp_le(tmp[1].fY, clip.fBottom);
+            clamp_le(tmp[2].fY, clip.fBottom);
+            pts[1] = tmp[1];
+            pts[2] = tmp[2];
+        } else {
+            // if chopMonoQuadAtY failed, then we may have hit inexact numerics
+            // so we just clamp against the bottom
+            for (int i = 0; i < 3; i++) {
+                if (pts[i].fY > clip.fBottom) {
+                    pts[i].fY = clip.fBottom;
+                }
+            }
+        }
+    }
+}
+
+// srcPts[] must be monotonic in X and Y
+void SkEdgeClipper::clipMonoQuad(const SkPoint srcPts[3], const SkRect& clip) {
+    SkPoint pts[3];
+    bool reverse = sort_increasing_Y(pts, srcPts, 3);
+
+    // are we completely above or below
+    if (pts[2].fY <= clip.fTop || pts[0].fY >= clip.fBottom) {
+        return;
+    }
+    
+    // Now chop so that pts is contained within clip in Y
+    chop_quad_in_Y(pts, clip);
+
+    if (pts[0].fX > pts[2].fX) {
+        SkTSwap<SkPoint>(pts[0], pts[2]);
+        reverse = !reverse;
+    }
+    SkASSERT(pts[0].fX <= pts[1].fX);
+    SkASSERT(pts[1].fX <= pts[2].fX);
+
+    // Now chop in X has needed, and record the segments
+
+    if (pts[2].fX <= clip.fLeft) {  // wholly to the left
+        this->appendVLine(clip.fLeft, pts[0].fY, pts[2].fY, reverse);
+        return;
+    }
+    if (pts[0].fX >= clip.fRight) {  // wholly to the right
+        this->appendVLine(clip.fRight, pts[0].fY, pts[2].fY, reverse);
+        return;
+    }
+
+    SkScalar t;
+    SkPoint tmp[5]; // for SkChopQuadAt
+
+    // are we partially to the left
+    if (pts[0].fX < clip.fLeft) {
+        if (chopMonoQuadAtX(pts, clip.fLeft, &t)) {
+            SkChopQuadAt(pts, tmp, t);
+            this->appendVLine(clip.fLeft, tmp[0].fY, tmp[2].fY, reverse);
+            clamp_ge(tmp[2].fX, clip.fLeft);
+            clamp_ge(tmp[3].fX, clip.fLeft);
+            pts[0] = tmp[2];
+            pts[1] = tmp[3];
+        } else {
+            // if chopMonoQuadAtY failed, then we may have hit inexact numerics
+            // so we just clamp against the left
+            this->appendVLine(clip.fLeft, pts[0].fY, pts[2].fY, reverse);
+        }
+    }
+    
+    // are we partially to the right
+    if (pts[2].fX > clip.fRight) {
+        if (chopMonoQuadAtX(pts, clip.fRight, &t)) {
+            SkChopQuadAt(pts, tmp, t);
+            clamp_le(tmp[1].fX, clip.fRight);
+            clamp_le(tmp[2].fX, clip.fRight);
+            this->appendQuad(tmp, reverse);
+            this->appendVLine(clip.fRight, tmp[2].fY, tmp[4].fY, reverse);
+        } else {
+            // if chopMonoQuadAtY failed, then we may have hit inexact numerics
+            // so we just clamp against the right
+            this->appendVLine(clip.fRight, pts[0].fY, pts[3].fY, reverse);
+        }
+    } else {    // wholly inside the clip
+        this->appendQuad(pts, reverse);
+    }
+}
+
+bool SkEdgeClipper::clipQuad(const SkPoint srcPts[3], const SkRect& clip) {
+    fCurrPoint = fPoints;
+    fCurrVerb = fVerbs;
+
+    SkRect  bounds;
+    bounds.set(srcPts, 3);
+    
+    if (!quick_reject(bounds, clip)) {
+        SkPoint monoY[5];
+        int countY = SkChopQuadAtYExtrema(srcPts, monoY);
+        for (int y = 0; y <= countY; y++) {
+            SkPoint monoX[5];
+            int countX = SkChopQuadAtXExtrema(&monoY[y * 2], monoX);
+            for (int x = 0; x <= countX; x++) {
+                this->clipMonoQuad(&monoX[x * 2], clip);
+                SkASSERT(fCurrVerb - fVerbs < kMaxVerbs);
+                SkASSERT(fCurrPoint - fPoints <= kMaxPoints);
+            }
+        }
+    }
+
+    *fCurrVerb = SkPath::kDone_Verb;
+    fCurrPoint = fPoints;
+    fCurrVerb = fVerbs;
+    return SkPath::kDone_Verb != fVerbs[0];
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+static SkScalar eval_cubic_coeff(SkScalar A, SkScalar B, SkScalar C,
+                                 SkScalar D, SkScalar t) {
+    return SkScalarMulAdd(SkScalarMulAdd(SkScalarMulAdd(A, t, B), t, C), t, D);
+}
+
+/*  Given 4 cubic points (either Xs or Ys), and a target X or Y, compute the
+    t value such that cubic(t) = target
+ */
+static bool chopMonoCubicAt(SkScalar c0, SkScalar c1, SkScalar c2, SkScalar c3,
+                           SkScalar target, SkScalar* t) {
+ //   SkASSERT(c0 <= c1 && c1 <= c2 && c2 <= c3);
+    SkASSERT(c0 < target && target < c3);
+
+    SkScalar D = c0;
+    SkScalar A = c3 + 3*(c1 - c2) - c0;
+    SkScalar B = 3*(c2 - c1 - c1 + c0);
+    SkScalar C = 3*(c1 - c0);
+
+    SkScalar minT = 0;
+    SkScalar maxT = SK_Scalar1;
+    for (int i = 0; i < 8; i++) {
+        SkScalar mid = SkScalarAve(minT, maxT);
+        SkScalar coord = eval_cubic_coeff(A, B, C, D, mid);
+        if (coord < target) {
+            minT = mid;
+        } else {
+            maxT = mid;
+        }
+    }
+    *t = SkScalarAve(minT, maxT);
+    return true;
+}
+
+static bool chopMonoCubicAtY(SkPoint pts[4], SkScalar y, SkScalar* t) {
+    return chopMonoCubicAt(pts[0].fY, pts[1].fY, pts[2].fY, pts[3].fY, y, t);
+}
+
+static bool chopMonoCubicAtX(SkPoint pts[4], SkScalar x, SkScalar* t) {
+    return chopMonoCubicAt(pts[0].fX, pts[1].fX, pts[2].fX, pts[3].fX, x, t);
+}
+
+// Modify pts[] in place so that it is clipped in Y to the clip rect
+static void chop_cubic_in_Y(SkPoint pts[4], const SkRect& clip) {
+    SkScalar t;
+    SkPoint tmp[7]; // for SkChopCubicAt
+    
+    // are we partially above
+    if (pts[0].fY < clip.fTop) {
+        if (chopMonoCubicAtY(pts, clip.fTop, &t)) {
+            SkChopCubicAt(pts, tmp, t);
+            clamp_ge(tmp[3].fY, clip.fTop);
+            clamp_ge(tmp[4].fY, clip.fTop);
+            clamp_ge(tmp[5].fY, clip.fTop);
+            pts[0] = tmp[3];
+            pts[1] = tmp[4];
+            pts[2] = tmp[5];
+        } else {
+            // if chopMonoCubicAtY failed, then we may have hit inexact numerics
+            // so we just clamp against the top
+            for (int i = 0; i < 4; i++) {
+                clamp_ge(pts[i].fY, clip.fTop);
+            }
+        }
+    }
+    
+    // are we partially below
+    if (pts[3].fY > clip.fBottom) {
+        if (chopMonoCubicAtY(pts, clip.fBottom, &t)) {
+            SkChopCubicAt(pts, tmp, t);
+            clamp_le(tmp[1].fY, clip.fBottom);
+            clamp_le(tmp[2].fY, clip.fBottom);
+            clamp_le(tmp[3].fY, clip.fBottom);
+            pts[1] = tmp[1];
+            pts[2] = tmp[2];
+            pts[3] = tmp[3];
+        } else {
+            // if chopMonoCubicAtY failed, then we may have hit inexact numerics
+            // so we just clamp against the bottom
+            for (int i = 0; i < 4; i++) {
+                clamp_le(pts[i].fY, clip.fBottom);
+            }
+        }
+    }
+}
+
+// srcPts[] must be monotonic in X and Y
+void SkEdgeClipper::clipMonoCubic(const SkPoint src[4], const SkRect& clip) {
+    SkPoint pts[4];
+    bool reverse = sort_increasing_Y(pts, src, 4);
+    
+    // are we completely above or below
+    if (pts[3].fY <= clip.fTop || pts[0].fY >= clip.fBottom) {
+        return;
+    }
+    
+    // Now chop so that pts is contained within clip in Y
+    chop_cubic_in_Y(pts, clip);
+    
+    if (pts[0].fX > pts[3].fX) {
+        SkTSwap<SkPoint>(pts[0], pts[3]);
+        SkTSwap<SkPoint>(pts[1], pts[2]);
+        reverse = !reverse;
+    }
+    
+    // Now chop in X has needed, and record the segments
+    
+    if (pts[3].fX <= clip.fLeft) {  // wholly to the left
+        this->appendVLine(clip.fLeft, pts[0].fY, pts[3].fY, reverse);
+        return;
+    }
+    if (pts[0].fX >= clip.fRight) {  // wholly to the right
+        this->appendVLine(clip.fRight, pts[0].fY, pts[3].fY, reverse);
+        return;
+    }
+    
+    SkScalar t;
+    SkPoint tmp[7];
+    
+    // are we partially to the left
+    if (pts[0].fX < clip.fLeft) {
+        if (chopMonoCubicAtX(pts, clip.fLeft, &t)) {
+            SkChopCubicAt(pts, tmp, t);
+            this->appendVLine(clip.fLeft, tmp[0].fY, tmp[3].fY, reverse);
+            clamp_ge(tmp[3].fX, clip.fLeft);
+            clamp_ge(tmp[4].fX, clip.fLeft);
+            clamp_ge(tmp[5].fX, clip.fLeft);
+            pts[0] = tmp[3];
+            pts[1] = tmp[4];
+            pts[2] = tmp[5];
+        } else {
+            // if chopMonocubicAtY failed, then we may have hit inexact numerics
+            // so we just clamp against the left
+            this->appendVLine(clip.fLeft, pts[0].fY, pts[3].fY, reverse);
+        }
+    }
+    
+    // are we partially to the right
+    if (pts[3].fX > clip.fRight) {
+        if (chopMonoCubicAtX(pts, clip.fRight, &t)) {
+            SkChopCubicAt(pts, tmp, t);
+            clamp_le(tmp[1].fX, clip.fRight);
+            clamp_le(tmp[2].fX, clip.fRight);
+            clamp_le(tmp[3].fX, clip.fRight);
+            this->appendCubic(tmp, reverse);
+            this->appendVLine(clip.fRight, tmp[3].fY, tmp[6].fY, reverse);
+        } else {
+            // if chopMonoCubicAtX failed, then we may have hit inexact numerics
+            // so we just clamp against the right
+            this->appendVLine(clip.fRight, pts[0].fY, pts[3].fY, reverse);
+        }
+    } else {    // wholly inside the clip
+        this->appendCubic(pts, reverse);
+    }
+}
+
+bool SkEdgeClipper::clipCubic(const SkPoint srcPts[4], const SkRect& clip) {
+    fCurrPoint = fPoints;
+    fCurrVerb = fVerbs;
+    
+    SkRect  bounds;
+    bounds.set(srcPts, 4);
+    
+    if (!quick_reject(bounds, clip)) {
+        SkPoint monoY[10];
+        int countY = SkChopCubicAtYExtrema(srcPts, monoY);
+        for (int y = 0; y <= countY; y++) {
+        //    sk_assert_monotonic_y(&monoY[y * 3], 4);
+            SkPoint monoX[10];
+            int countX = SkChopCubicAtXExtrema(&monoY[y * 3], monoX);
+            for (int x = 0; x <= countX; x++) {
+            //    sk_assert_monotonic_y(&monoX[x * 3], 4);
+            //    sk_assert_monotonic_x(&monoX[x * 3], 4);
+                this->clipMonoCubic(&monoX[x * 3], clip);
+                SkASSERT(fCurrVerb - fVerbs < kMaxVerbs);
+                SkASSERT(fCurrPoint - fPoints <= kMaxPoints);
+            }
+        }
+    }
+    
+    *fCurrVerb = SkPath::kDone_Verb;
+    fCurrPoint = fPoints;
+    fCurrVerb = fVerbs;
+    return SkPath::kDone_Verb != fVerbs[0];
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+void SkEdgeClipper::appendVLine(SkScalar x, SkScalar y0, SkScalar y1,
+                                bool reverse) {
+    *fCurrVerb++ = SkPath::kLine_Verb;
+    
+    if (reverse) {
+        SkTSwap<SkScalar>(y0, y1);
+    }
+    fCurrPoint[0].set(x, y0);
+    fCurrPoint[1].set(x, y1);
+    fCurrPoint += 2;
+}
+
+void SkEdgeClipper::appendQuad(const SkPoint pts[3], bool reverse) {
+    *fCurrVerb++ = SkPath::kQuad_Verb;
+    
+    if (reverse) {
+        fCurrPoint[0] = pts[2];
+        fCurrPoint[2] = pts[0];
+    } else {
+        fCurrPoint[0] = pts[0];
+        fCurrPoint[2] = pts[2];
+    }
+    fCurrPoint[1] = pts[1];
+    fCurrPoint += 3;
+}
+
+void SkEdgeClipper::appendCubic(const SkPoint pts[4], bool reverse) {
+    *fCurrVerb++ = SkPath::kCubic_Verb;
+    
+    if (reverse) {
+        for (int i = 0; i < 4; i++) {
+            fCurrPoint[i] = pts[3 - i];
+        }
+    } else {
+        memcpy(fCurrPoint, pts, 4 * sizeof(SkPoint));
+    }
+    fCurrPoint += 4;
+}
+
+SkPath::Verb SkEdgeClipper::next(SkPoint pts[]) {
+    SkPath::Verb verb = *fCurrVerb;
+
+    switch (verb) {
+        case SkPath::kLine_Verb:
+            memcpy(pts, fCurrPoint, 2 * sizeof(SkPoint));
+            fCurrPoint += 2;
+            fCurrVerb += 1;
+            break;
+        case SkPath::kQuad_Verb:
+            memcpy(pts, fCurrPoint, 3 * sizeof(SkPoint));
+            fCurrPoint += 3;
+            fCurrVerb += 1;
+            break;
+        case SkPath::kCubic_Verb:
+            memcpy(pts, fCurrPoint, 4 * sizeof(SkPoint));
+            fCurrPoint += 4;
+            fCurrVerb += 1;
+            break;
+        case SkPath::kDone_Verb:
+            break;
+        default:
+            SkASSERT(!"unexpected verb in quadclippper2 iter");
+            break;
+    }
+    return verb;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+#ifdef SK_DEBUG
+static void assert_monotonic(const SkScalar coord[], int count) {
+    if (coord[0] > coord[(count - 1) * 2]) {
+        for (int i = 1; i < count; i++) {
+            SkASSERT(coord[2 * (i - 1)] >= coord[i * 2]);
+        }
+    } else if (coord[0] < coord[(count - 1) * 2]) {
+        for (int i = 1; i < count; i++) {
+            SkASSERT(coord[2 * (i - 1)] <= coord[i * 2]);
+        }
+    } else {
+        for (int i = 1; i < count; i++) {
+            SkASSERT(coord[2 * (i - 1)] == coord[i * 2]);
+        }
+    }
+}
+
+void sk_assert_monotonic_y(const SkPoint pts[], int count) {
+    if (count > 1) {
+        assert_monotonic(&pts[0].fY, count);
+    }
+}
+
+void sk_assert_monotonic_x(const SkPoint pts[], int count) {
+    if (count > 1) {
+        assert_monotonic(&pts[0].fX, count);
+    }
+}
+#endif