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, 154 insertions, 0 deletions

diff --git a/src/core/SkEdgeBuilder.cpp b/src/core/SkEdgeBuilder.cpp
new file mode 100644
index 0000000000..0f8848809c
--- /dev/null
+++ b/src/core/SkEdgeBuilder.cpp
@@ -0,0 +1,154 @@
+#include "SkEdgeBuilder.h"
+#include "SkPath.h"
+#include "SkEdge.h"
+#include "SkEdgeClipper.h"
+#include "SkLineClipper.h"
+#include "SkGeometry.h"
+
+SkEdgeBuilder::SkEdgeBuilder() : fAlloc(16*1024) {}
+
+template <typename T> static T* typedAllocThrow(SkChunkAlloc& alloc) {
+    return static_cast<T*>(alloc.allocThrow(sizeof(T)));
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+void SkEdgeBuilder::addLine(const SkPoint pts[]) {
+    SkEdge* edge = typedAllocThrow<SkEdge>(fAlloc);
+    if (edge->setLine(pts[0], pts[1], NULL, fShiftUp)) {
+        fList.push(edge);
+    } else {
+        // TODO: unallocate edge from storage...
+    }
+}
+
+void SkEdgeBuilder::addQuad(const SkPoint pts[]) {
+    SkQuadraticEdge* edge = typedAllocThrow<SkQuadraticEdge>(fAlloc);
+    if (edge->setQuadratic(pts, fShiftUp)) {
+        fList.push(edge);
+    } else {
+        // TODO: unallocate edge from storage...
+    }
+}
+
+void SkEdgeBuilder::addCubic(const SkPoint pts[]) {
+    SkCubicEdge* edge = typedAllocThrow<SkCubicEdge>(fAlloc);
+    if (edge->setCubic(pts, NULL, fShiftUp)) {
+        fList.push(edge);
+    } else {
+        // TODO: unallocate edge from storage...
+    }
+}
+
+void SkEdgeBuilder::addClipper(SkEdgeClipper* clipper) {
+    SkPoint      pts[4];
+    SkPath::Verb verb;
+
+    while ((verb = clipper->next(pts)) != SkPath::kDone_Verb) {
+        switch (verb) {
+            case SkPath::kLine_Verb:
+                this->addLine(pts);
+                break;
+            case SkPath::kQuad_Verb:
+                this->addQuad(pts);
+                break;
+            case SkPath::kCubic_Verb:
+                this->addCubic(pts);
+                break;
+            default:
+                break;
+        }
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+static void setShiftedClip(SkRect* dst, const SkIRect& src, int shift) {
+    dst->set(SkIntToScalar(src.fLeft >> shift),
+             SkIntToScalar(src.fTop >> shift),
+             SkIntToScalar(src.fRight >> shift),
+             SkIntToScalar(src.fBottom >> shift));
+}
+
+int SkEdgeBuilder::build(const SkPath& path, const SkIRect* iclip,
+                         int shiftUp) {
+    fAlloc.reset();
+    fList.reset();
+    fShiftUp = shiftUp;
+
+    SkPath::Iter    iter(path, true);
+    SkPoint         pts[4];
+    SkPath::Verb    verb;
+
+    if (iclip) {
+        SkRect clip;
+        setShiftedClip(&clip, *iclip, shiftUp);
+        SkEdgeClipper clipper;
+
+        while ((verb = iter.next(pts)) != SkPath::kDone_Verb) {
+            switch (verb) {
+                case SkPath::kMove_Verb:
+                case SkPath::kClose_Verb:
+                    // we ignore these, and just get the whole segment from
+                    // the corresponding line/quad/cubic verbs
+                    break;
+                case SkPath::kLine_Verb: {
+                    SkPoint lines[SkLineClipper::kMaxPoints];
+                    int lineCount = SkLineClipper::ClipLine(pts, clip, lines);
+                    for (int i = 0; i < lineCount; i++) {
+                        this->addLine(&lines[i]);
+                    }
+                    break;
+                }
+                case SkPath::kQuad_Verb:
+                    if (clipper.clipQuad(pts, clip)) {
+                        this->addClipper(&clipper);
+                    }
+                    break;
+                case SkPath::kCubic_Verb:
+                    if (clipper.clipCubic(pts, clip)) {
+                        this->addClipper(&clipper);
+                    }
+                    break;
+                default:
+                    SkASSERT(!"unexpected verb");
+                    break;
+            }
+        }
+    } else {
+        while ((verb = iter.next(pts)) != SkPath::kDone_Verb) {
+            switch (verb) {
+                case SkPath::kMove_Verb:
+                case SkPath::kClose_Verb:
+                    // we ignore these, and just get the whole segment from
+                    // the corresponding line/quad/cubic verbs
+                    break;
+                case SkPath::kLine_Verb:
+                    this->addLine(pts);
+                    break;
+                case SkPath::kQuad_Verb: {
+                    SkPoint monoX[5];
+                    int n = SkChopQuadAtYExtrema(pts, monoX);
+                    for (int i = 0; i <= n; i++) {
+                        this->addQuad(&monoX[i * 2]);
+                    }
+                    break;
+                }
+                case SkPath::kCubic_Verb: {
+                    SkPoint monoY[10];
+                    int n = SkChopCubicAtYExtrema(pts, monoY);
+                    for (int i = 0; i <= n; i++) {
+                        this->addCubic(&monoY[i * 3]);
+                    }
+                    break;
+                }
+                default:
+                    SkASSERT(!"unexpected verb");
+                    break;
+            }
+        }
+    }
+    return fList.count();
+}
+
+