Add --flip-x argument to optionally mirror the output.

When used with the usual cookie cutter profile, this makes the input shape correspond to the shape of the final cookie rather than the shape of the cookie cutter sitting upside down on the printer.

This doesn't really belong in here (sweep should not know anything about cookie cutters, but just process the input files as they are), but it was the easiest point to insert it in the Inkscape integration.

Author: cwalther

sweep.cpp

@@ -379,21 +379,34 @@ void writeStlTriangle(const Vertex& v1, const Vertex& v2, const Vertex& v3, FILE
 }
 
 int main(int argc, char **argv) {
-	if (argc < 4) {
-		fprintf(stderr, "Usage: %s <crosssection.png> <shape.png> <output.stl>\n\n"
+	const char* filenames[3] = {NULL, NULL, NULL};
+	bool flipX = false;
+	for (int i = 1, j = 0; i < argc; i++) {
+		if (strcmp(argv[i], "--flip-x") == 0) {
+			flipX = !flipX;
+		}
+		else {
+			if (j < 3) filenames[j++] = argv[i];
+		}
+	}
+
+	if (filenames[2] == NULL) {
+		fprintf(stderr, "Usage: %s [--flip-x] <crosssection.png> <shape.png> <output.stl>\n\n"
 			"Sweep (extrude) a cross-section shape along the edge of a shape to make a solid.\n"
 			"Input: black = inside, white or transparent = outside, antialiasing recommended.\n"
 			"Left half of cross section goes inside, right half outside.\n"
-			"Output is scaled according to resolution of cross-section image.\n\n"
-			"Version 1.1\n"
+			"Output is scaled according to resolution of cross-section image.\n"
+			"--flip-x: Mirror output in x direction.\n\n"
+			"Version 1.2\n"
 			"Copyright (c) 2013-2015 Christian Walther <cwalther%cgmx.ch>\n"
 			"https://github.com/cwalther/cookie-cutter-sweeper\n", argv[0], '@');
 		return 2;
 	}
+
 	try {
 		// compute the 2D distance fields of section and shape
-		FloatMatrix section = distanceField(readPng(argv[1]), 2);
-		FloatMatrix shape = distanceField(readPng(argv[2]), (section.getWidth() + 1)/2);
+		FloatMatrix section = distanceField(readPng(filenames[0]), 2);
+		FloatMatrix shape = distanceField(readPng(filenames[1]), (section.getWidth() + 1)/2);
 
 		// initialization for working in z-slices, keeping only the last two slices in memory
 		FloatMatrix slice1(shape.getWidth(), shape.getHeight());
@@ -460,7 +473,7 @@ int main(int argc, char **argv) {
 								v.count++;
 								face.index[j] = vi - 1;
 							}
-							if (q >= 0) {
+							if ((q >= 0) != flipX) {
 								// outwards-pointing edge, reverse face orientation
 								unsigned int t = face.index[1];
 								face.index[1] = face.index[3];
@@ -482,23 +495,25 @@ int main(int argc, char **argv) {
 			// finish averaging
 			it->normalize();
 			// - invert in y and z directions to convert from upside-down image coordinate system
+			// - invert in x direction if requested
 			// - shift by (1, 1, 1) to ensure all coordinates are positive as required by STL spec
 			// - scale by the resolution read from the section image, if any
+			if (flipX) it->xsum = shape.getWidth() - it->xsum;
 			it->xsum = (it->xsum + 1.0f)/section.getScale();
 			it->ysum = (shape.getHeight() - it->ysum + 1.0f)/section.getScale();
 			it->zsum = (section.getHeight() - it->zsum + 1.0f)/section.getScale();
 		}
 
 		// now we have a mesh in a typical list-of-vertex-coordinates + list-of-faces-by-vertex-indices form, save it in STL format, which only stores individual triangles
 		FILE* of;
-		if (strcmp(argv[3], "-") == 0) {
+		if (strcmp(filenames[2], "-") == 0) {
 			of = stdout;
 		}
 		else {
-			of = fopen(argv[3], "wb");
+			of = fopen(filenames[2], "wb");
 		}
 		if (of == NULL) {
-			fprintf(stderr, "cannot open file %s: %s\n", argv[3], strerror(errno));
+			fprintf(stderr, "cannot open file %s: %s\n", filenames[2], strerror(errno));
 			return 1;
 		}
 		for (int i = 0; i < 80; i++) fputc(0, of);