Skia integration - preprocessing of shape geometry

.gitattributes

@@ -2,3 +2,4 @@
 include/** linguist-vendored
 lib/** linguist-vendored
 freetype/** linguist-vendored
+skia/** linguist-vendored

.gitignore

@@ -1,11 +1,11 @@
-Debug/
-Release/
-Release OpenMP/
-Debug Library/
-Release Library/
-Release Library OpenMP/
-x86/
-x64/
+/Debug/
+/Release/
+/Release OpenMP/
+/Debug Library/
+/Release Library/
+/Release Library OpenMP/
+/x86/
+/x64/
 .vs/
 *.exe
 *.zip
@@ -17,9 +17,11 @@ x64/
 *.suo
 *.VC.opendb
 *.VC.db
-bin/*.lib
+/bin/*.lib
 output.png
 render.png
 out/
 build/
 build_xcode/
+skia/win32/
+skia/win64/

CHANGELOG.md

@@ -1,4 +1,23 @@
 
+## Version 1.8 (2020-10-17)
+
+- Integrated the Skia library into the project, which is used to preprocess the shape geometry and eliminate any self-intersections and other irregularities previously unsupported by the software
+    - The scanline pass and overlapping contour mode is made obsolete by this step and has been disabled by default. The preprocess step can be disabled by the new `-nopreprocess` switch and the former enabled by `-scanline` and `-overlap` respectively.
+    - The project can be built without the Skia library, forgoing the geometry preprocessing feature. This is controlled by the macro definition `MSDFGEN_USE_SKIA`
+- Significantly improved performance of the core algorithm by reusing results from previously computed pixels
+- Introduced an additional error correction routine which eliminates MSDF artifacts by analytically predicting results of bilinear interpolation
+- Added the possibility to load font glyphs by their index rather than a Unicode value (use the prefix `g` before the character code in `-font` argument)
+- Added `-distanceshift` argument that can be used to adjust the center of the distance range in the output distance field
+- Fixed several errors in the evaluation of curve distances
+- Fixed an issue with paths containing convergent corners (those whose inner angle is zero)
+- The algorithm for pseudo-distance computation slightly changed, fixing certain rare edge cases and improving consistency
+- Added the ability to supply own `FT_Face` handle to the msdfgen library
+- Minor refactor of the core algorithm
+
+### Version 1.7.1 (2020-03-09)
+
+- Fixed an edge case bug in scanline rasterization
+
 ## Version 1.7 (2020-03-07)
 
 - Added `mtsdf` mode - a combination of `msdf` with `sdf` in the alpha channel

CMakeLists.txt

@@ -1,9 +1,10 @@
 cmake_minimum_required(VERSION 3.10)
 
-project(msdfgen VERSION 1.7.1 LANGUAGES CXX)
+project(msdfgen VERSION 1.8 LANGUAGES CXX)
 option(MSDFGEN_BUILD_MSDFGEN_STANDALONE "Build the msdfgen standalone executable" ON)
 option(MSDFGEN_USE_OPENMP "Build with OpenMP support for multithreaded code" OFF)
 option(MSDFGEN_USE_CPP11 "Build with C++11 enabled" ON)
+option(MSDFGEN_USE_SKIA "Build with the Skia library" OFF)
 option(FREETYPE_WITH_PNG "Link libpng and zlib because FreeType is configured to require it" OFF)
 option(FREETYPE_WITH_HARFBUZZ "Link HarfBuzz because FreeType is configured to require it" OFF)
 
@@ -71,6 +72,12 @@ if(MSDFGEN_USE_OPENMP)
 	target_compile_definitions(msdfgen PRIVATE MSDFGEN_USE_OPENMP)
 endif()
 
+if(MSDFGEN_USE_SKIA)
+	find_package(Skia REQUIRED)
+	target_link_libraries(msdfgen-ext PRIVATE Skia::Skia)
+	target_compile_definitions(msdfgen-ext PUBLIC MSDFGEN_USE_SKIA)
+endif()
+
 add_library(msdfgen-ext ${msdfgen-ext_SOURCES} ${msdfgen-ext_PUBLIC_HEADERS} ${msdfgen-ext_PRIVATE_HEADERS} "./msdfgen-ext.h")
 add_library(msdfgen::msdfgen-ext ALIAS msdfgen-ext)
 set_target_properties(msdfgen-ext PROPERTIES

Msdfgen.vcxproj.filters

@@ -120,6 +120,9 @@
     <ClInclude Include="core\msdf-edge-artifact-patcher.h">
       <Filter>Core</Filter>
     </ClInclude>
+    <ClInclude Include="ext\resolve-shape-geometry.h">
+      <Filter>Extensions</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <ClCompile Include="main.cpp">
@@ -200,6 +203,9 @@
     <ClCompile Include="core\msdf-edge-artifact-patcher.cpp">
       <Filter>Core</Filter>
     </ClCompile>
+    <ClCompile Include="ext\resolve-shape-geometry.cpp">
+      <Filter>Extensions</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ResourceCompile Include="Msdfgen.rc">

README.md

@@ -26,7 +26,8 @@ Extensions contain utilities for loading fonts and SVG files, as well as saving
 Those are exposed by the [msdfgen-ext.h](msdfgen-ext.h) header. This module uses
 [FreeType](http://www.freetype.org/),
 [TinyXML2](http://www.grinninglizard.com/tinyxml2/),
-and [LodePNG](http://lodev.org/lodepng/).
+[LodePNG](http://lodev.org/lodepng/),
+and (optionally) [Skia](https://skia.org/).
 
 Additionally, there is the [main.cpp](main.cpp), which wraps the functionality into
 a comprehensive standalone console program. To start using the program immediately,

ext/resolve-shape-geometry.cpp

@@ -0,0 +1,89 @@
+
+#include "resolve-shape-geometry.h"
+
+#ifdef MSDFGEN_USE_SKIA
+
+#include <core/SkPath.h>
+#include <pathops/SkPathOps.h>
+#include "../core/Vector2.h"
+#include "../core/edge-segments.h"
+#include "../core/Contour.h"
+
+#ifdef _WIN32
+    #pragma comment(lib, "skia.lib")
+#endif
+
+namespace msdfgen {
+
+SkPoint pointToSkiaPoint(Point2 p) {
+    return SkPoint::Make((SkScalar) p.x, (SkScalar) p.y);
+}
+
+Point2 pointFromSkiaPoint(const SkPoint p) {
+    return Point2((double) p.x(), (double) p.y());
+}
+
+void shapeToSkiaPath(SkPath &skPath, const Shape &shape) {
+    for (std::vector<Contour>::const_iterator contour = shape.contours.begin(); contour != shape.contours.end(); ++contour) {
+        if (!contour->edges.empty()) {
+            skPath.moveTo(pointToSkiaPoint(contour->edges.front()->point(0)));
+            for (std::vector<EdgeHolder>::const_iterator edge = contour->edges.begin(); edge != contour->edges.end(); ++edge) {
+                {
+                    const LinearSegment *linearSegment = dynamic_cast<const LinearSegment *>(&**edge);
+                    if (linearSegment)
+                        skPath.lineTo(pointToSkiaPoint(linearSegment->p[1]));
+                } {
+                    const QuadraticSegment *quadraticSegment = dynamic_cast<const QuadraticSegment *>(&**edge);
+                    if (quadraticSegment)
+                        skPath.quadTo(pointToSkiaPoint(quadraticSegment->p[1]), pointToSkiaPoint(quadraticSegment->p[2]));
+                } {
+                    const CubicSegment *cubicSegment = dynamic_cast<const CubicSegment *>(&**edge);
+                    if (cubicSegment)
+                        skPath.cubicTo(pointToSkiaPoint(cubicSegment->p[1]), pointToSkiaPoint(cubicSegment->p[2]), pointToSkiaPoint(cubicSegment->p[3]));
+                }
+            }
+        }
+    }
+}
+
+void shapeFromSkiaPath(Shape &shape, const SkPath &skPath) {
+    shape.contours.clear();
+    Contour *contour = &shape.addContour();
+    SkPath::Iter pathIterator(skPath, true);
+    SkPoint edgePoints[4];
+    for (SkPath::Verb op; (op = pathIterator.next(edgePoints)) != SkPath::kDone_Verb;) {
+        switch (op) {
+            case SkPath::kMove_Verb:
+                if (!contour->edges.empty())
+                    contour = &shape.addContour();
+                break;
+            case SkPath::kLine_Verb:
+                contour->addEdge(new LinearSegment(pointFromSkiaPoint(edgePoints[0]), pointFromSkiaPoint(edgePoints[1])));
+                break;
+            case SkPath::kQuad_Verb:
+                contour->addEdge(new QuadraticSegment(pointFromSkiaPoint(edgePoints[0]), pointFromSkiaPoint(edgePoints[1]), pointFromSkiaPoint(edgePoints[2])));
+                break;
+            case SkPath::kCubic_Verb:
+                contour->addEdge(new CubicSegment(pointFromSkiaPoint(edgePoints[0]), pointFromSkiaPoint(edgePoints[1]), pointFromSkiaPoint(edgePoints[2]), pointFromSkiaPoint(edgePoints[3])));
+                break;
+            default:;
+        }
+    }
+    if (contour->edges.empty())
+        shape.contours.pop_back();
+}
+
+bool resolveShapeGeometry(Shape &shape) {
+    SkPath skPath;
+    shapeToSkiaPath(skPath, shape);
+    if (!Simplify(skPath, &skPath))
+        return false;
+    // Skia's AsWinding doesn't seem to work for unknown reasons
+    shapeFromSkiaPath(shape, skPath);
+    shape.orientContours();
+    return true;
+}
+
+}
+
+#endif

ext/resolve-shape-geometry.h

@@ -0,0 +1,15 @@
+
+#pragma once
+
+#include "../core/Shape.h"
+
+#ifdef MSDFGEN_USE_SKIA
+
+namespace msdfgen {
+
+/// Resolves any intersections within the shape by subdividing its contours using the Skia library and makes sure its contours have a consistent winding.
+bool resolveShapeGeometry(Shape &shape);
+
+}
+
+#endif

main.cpp

@@ -1,6 +1,6 @@
 
 /*
- * MULTI-CHANNEL SIGNED DISTANCE FIELD GENERATOR v1.7 (2020-03-07) - standalone console program
+ * MULTI-CHANNEL SIGNED DISTANCE FIELD GENERATOR v1.8 (2020-10-17) - standalone console program
  * --------------------------------------------------------------------------------------------
  * A utility by Viktor Chlumsky, (c) 2014 - 2020
  *
@@ -252,10 +252,24 @@ static const char * writeOutput(const BitmapConstRef<float, N> &bitmap, const ch
     return NULL;
 }
 
+#if defined(MSDFGEN_USE_SKIA) && defined(MSDFGEN_USE_OPENMP)
+    #define TITLE_SUFFIX    " with Skia & OpenMP"
+    #define EXTRA_UNDERLINE "-------------------"
+#elif defined(MSDFGEN_USE_SKIA)
+    #define TITLE_SUFFIX    " with Skia"
+    #define EXTRA_UNDERLINE "----------"
+#elif defined(MSDFGEN_USE_OPENMP)
+    #define TITLE_SUFFIX    " with OpenMP"
+    #define EXTRA_UNDERLINE "------------"
+#else
+    #define TITLE_SUFFIX
+    #define EXTRA_UNDERLINE
+#endif
+
 static const char *helpText =
     "\n"
-    "Multi-channel signed distance field generator by Viktor Chlumsky v" MSDFGEN_VERSION "\n"
-    "---------------------------------------------------------------------\n"
+    "Multi-channel signed distance field generator by Viktor Chlumsky v" MSDFGEN_VERSION TITLE_SUFFIX "\n"
+    "---------------------------------------------------------------------" EXTRA_UNDERLINE "\n"
     "  Usage: msdfgen"
     #ifdef _WIN32
         ".exe"
@@ -273,14 +287,16 @@ static const char *helpText =
     "  -defineshape <definition>\n"
         "\tDefines input shape using the ad-hoc text definition.\n"
     "  -font <filename.ttf> <character code>\n"
-        "\tLoads a single glyph from the specified font file. Format of character code is '?', 63, 0x3F (Unicode value), or g34 (glyph index).\n"
+        "\tLoads a single glyph from the specified font file.\n"
+        "\tFormat of character code is '?', 63, 0x3F (Unicode value), or g34 (glyph index).\n"
     "  -shapedesc <filename.txt>\n"
         "\tLoads text shape description from a file.\n"
     "  -stdin\n"
         "\tReads text shape description from the standard input.\n"
     "  -svg <filename.svg>\n"
         "\tLoads the last vector path found in the specified SVG file.\n"
     "\n"
+    // Keep alphabetical order!
     "OPTIONS\n"
     "  -angle <angle>\n"
         "\tSpecifies the minimum angle between adjacent edges to be considered a corner. Append D for degrees.\n"
@@ -310,22 +326,35 @@ static const char *helpText =
         "\tDisplays this help.\n"
     "  -legacy\n"
         "\tUses the original (legacy) distance field algorithms.\n"
+#ifdef MSDFGEN_USE_SKIA
+    "  -nopreprocess\n"
+        "\tDisables path preprocessing which resolves self-intersections and overlapping contours.\n"
+#else
     "  -nooverlap\n"
         "\tDisables resolution of overlapping contours.\n"
     "  -noscanline\n"
         "\tDisables the scanline pass, which corrects the distance field's signs according to the selected fill rule.\n"
+#endif
     "  -o <filename>\n"
         "\tSets the output file name. The default value is \"output.png\".\n"
+#ifdef MSDFGEN_USE_SKIA
+    "  -overlap\n"
+        "\tSwitches to distance field generator with support for overlapping contours.\n"
+#endif
     "  -printmetrics\n"
         "\tPrints relevant metrics of the shape to the standard output.\n"
     "  -pxrange <range>\n"
         "\tSets the width of the range between the lowest and highest signed distance in pixels.\n"
     "  -range <range>\n"
         "\tSets the width of the range between the lowest and highest signed distance in shape units.\n"
     "  -reverseorder\n"
-        "\tGenerates the distance field as if shape vertices were in reverse order.\n"
+        "\tGenerates the distance field as if the shape's vertices were in reverse order.\n"
     "  -scale <scale>\n"
         "\tSets the scale used to convert shape units to pixels.\n"
+#ifdef MSDFGEN_USE_SKIA
+    "  -scanline\n"
+        "\tPerforms an additional scanline pass to fix the signs of the distances.\n"
+#endif
     "  -seed <n>\n"
         "\tSets the random seed for edge coloring heuristic.\n"
     "  -size <width> <height>\n"
@@ -362,8 +391,15 @@ int main(int argc, const char * const *argv) {
         METRICS
     } mode = MULTI;
     bool legacyMode = false;
-    bool overlapSupport = true;
-    bool scanlinePass = true;
+    bool geometryPreproc = (
+        #ifdef MSDFGEN_USE_SKIA
+            true
+        #else
+            false
+        #endif
+    );
+    bool overlapSupport = !geometryPreproc;
+    bool scanlinePass = !geometryPreproc;
     FillRule fillRule = FILL_NONZERO;
     Format format = AUTO;
     const char *input = NULL;
@@ -477,11 +513,26 @@ int main(int argc, const char * const *argv) {
             argPos += 1;
             continue;
         }
+        ARG_CASE("-nopreprocess", 0) {
+            geometryPreproc = false;
+            argPos += 1;
+            continue;
+        }
+        ARG_CASE("-preprocess", 0) {
+            geometryPreproc = true;
+            argPos += 1;
+            continue;
+        }
         ARG_CASE("-nooverlap", 0) {
             overlapSupport = false;
             argPos += 1;
             continue;
         }
+        ARG_CASE("-overlap", 0) {
+            overlapSupport = true;
+            argPos += 1;
+            continue;
+        }
         ARG_CASE("-noscanline", 0) {
             scanlinePass = false;
             argPos += 1;
@@ -493,6 +544,7 @@ int main(int argc, const char * const *argv) {
             continue;
         }
         ARG_CASE("-fillrule", 1) {
+            scanlinePass = true;
             if (!strcmp(argv[argPos+1], "nonzero")) fillRule = FILL_NONZERO;
             else if (!strcmp(argv[argPos+1], "evenodd") || !strcmp(argv[argPos+1], "odd")) fillRule = FILL_ODD;
             else if (!strcmp(argv[argPos+1], "positive")) fillRule = FILL_POSITIVE;
@@ -749,6 +801,14 @@ int main(int argc, const char * const *argv) {
     // Validate and normalize shape
     if (!shape.validate())
         ABORT("The geometry of the loaded shape is invalid.");
+    if (geometryPreproc) {
+        #ifdef MSDFGEN_USE_SKIA
+            if (!resolveShapeGeometry(shape))
+                puts("Shape geometry preprocessing failed, skipping.");
+        #else
+            ABORT("Shape geometry preprocessing (-preprocess) is not available in this version because the Skia library is not present.");
+        #endif
+    }
     shape.normalize();
     if (yFlip)
         shape.inverseYAxis = !shape.inverseYAxis;