add quadclipping utility, plus sample test

git-svn-id: http://skia.googlecode.com/svn/trunk@429 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 225 insertions, 4 deletions

diff --git a/src/core/SkQuadClipper.cpp b/src/core/SkQuadClipper.cpp
index 7521bdc7fd..9d76298cae 100644
--- a/src/core/SkQuadClipper.cpp
+++ b/src/core/SkQuadClipper.cpp
@@ -17,14 +17,15 @@
 #include "SkQuadClipper.h"
 #include "SkGeometry.h"
 
-static bool chopMonoQuadAtY(SkPoint pts[3], SkScalar y, SkScalar* t) {
+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 = pts[0].fY - pts[1].fY - pts[1].fY + pts[2].fY;
-    SkScalar B = 2*(pts[1].fY - pts[0].fY);
-    SkScalar C = pts[0].fY - y;
+    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);
@@ -35,6 +36,14 @@ static bool chopMonoQuadAtY(SkPoint pts[3], SkScalar y, SkScalar* t) {
     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);
+}
+
 SkQuadClipper::SkQuadClipper() {}
 
 void SkQuadClipper::setClip(const SkIRect& clip) {
@@ -111,3 +120,215 @@ bool SkQuadClipper::clipQuad(const SkPoint srcPts[3], SkPoint dst[3]) {
     return true;
 }
 
+///////////////////////////////////////////////////////////////////////////////
+
+// 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);
+            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);
+            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;
+                }
+            }
+        }
+    }
+}
+
+/*  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[]) {
+    // we need the data to be monotonically increasing in Y
+    if (src[0].fY > src[2].fY) {
+        SkASSERT(src[0].fY >= src[1].fY);
+        SkASSERT(src[1].fY >= src[2].fY);
+        dst[0] = src[2];
+        dst[1] = src[1];
+        dst[2] = src[0];
+        return true;
+    } else {
+        SkASSERT(src[2].fY >= src[1].fY);
+        SkASSERT(src[1].fY >= src[0].fY);
+        memcpy(dst, src, 3 * sizeof(SkPoint));
+        return false;
+    }
+}
+
+// srcPts[] must be monotonic in X and Y
+void SkQuadClipper2::clipMonoQuad(const SkPoint srcPts[3], const SkRect& clip) {
+    SkPoint pts[3];
+    bool reverse = sort_increasing_Y(pts, srcPts);
+
+    // 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);
+            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);
+            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);
+    }
+}
+
+static bool quick_reject_quad(const SkPoint srcPts[3], const SkRect& clip) {
+    return (srcPts[0].fY <= clip.fTop &&
+            srcPts[1].fY <= clip.fTop &&
+            srcPts[2].fY <= clip.fTop)
+            ||
+           (srcPts[0].fY >= clip.fBottom &&
+            srcPts[1].fY >= clip.fBottom &&
+            srcPts[2].fY >= clip.fBottom);
+}
+
+bool SkQuadClipper2::clipQuad(const SkPoint srcPts[3], const SkRect& clip) {
+    fCurrPoint = fPoints;
+    fCurrVerb = fVerbs;
+
+    if (!quick_reject_quad(srcPts, 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);
+            SkASSERT(countY + countX <= 3);
+            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];
+}
+
+void SkQuadClipper2::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 SkQuadClipper2::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;
+}
+
+SkPath::Verb SkQuadClipper2::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::kDone_Verb:
+            break;
+        default:
+            SkASSERT(!"unexpected verb in quadclippper2 iter");
+            break;
+    }
+    return verb;
+}
+