1 files changed, 116 insertions, 0 deletions
diff --git a/rtgrpblib_draw_linear_bezier.c b/rtgrpblib_draw_linear_bezier.c
new file mode 100644
index 0000000..5c83591
--- /dev/null
+++ b/rtgrpblib_draw_linear_bezier.c
@@ -0,0 +1,116 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+#ifndef TEST
+
+
+void
+rtgrpblib_draw_linear_bezier(RASTER *restrict raster, double x1, double y1, double x2, double y2)
+{
+	double w, h, dx, dy, x, y;
+	int xdir, ydir;
+
+	dx = x2 - x1;
+	dy = y2 - y1;
+	xdir = SIGNUM(dx);
+	ydir = SIGNUM(dy);
+
+	if (!ydir) {
+		/* For horizontal lines, it is enough that we have the
+		 * corners mapped onto the raster, which we must have
+		 * since a glyph cannot just contain a line, but outlines:
+		 * in `fill`, the line will not make a contribution because
+		 * `.opposite_coverage` for each cell will be zero, and
+		 * consequentially, `.cell_coverage` will also be zero */
+		return;
+	}
+
+	/* We cut of everything above and below the raster,
+	 * as these do not contribute to the result */
+	h = (double)raster->height;
+	if (y1 < 0 && y2 < 0)
+		return;
+	if (y1 >= h && y2 >= h)
+		return;
+	if (y1 < 0 && y2 >= 0) {
+		x1 = x1 + (0 - y1) * dx / dy;
+		y1 = 0;
+	} else if (y2 < 0 && y1 >= 0) {
+		x2 = x1 + (0 - y1) * dx / dy;
+		y2 = 0;
+	}
+	if (y1 < h && y2 >= h) {
+		x2 = x1 + (h - y1) * dx / dy;
+		y2 = h;
+	} else if (y2 < h && y1 >= h) {
+		x1 = x1 + (h - y1) * dx / dy;
+		y1 = h;
+	}
+
+	/* Dealing with the left and the right section
+	 * is not as simple as `fill` assumes that the
+	 * sum of each line's `.opposite_coverage` is 0.
+	 * Therefore must must identify the parts of the
+	 * line that are left of the raster, right of
+	 * the raster, and inside the raster. The parts
+	 * that are outside the raster are move to the
+	 * edge, or rather their show on the edges are
+	 * used. */
+	w = (double)raster->width;
+	if (x1 <= 0 && x2 <= 0) {
+		draw_vertical_line(raster, 0, y1, y2, ydir);
+		return;
+	}
+	if (x1 >= w && x2 >= w) {
+		draw_vertical_line_opposite_only(raster, raster->width - 1, y1, y2, ydir);
+		return;
+	}
+	if (x1 < 0 && x2 >= 0) {
+		y = y1 + (0 - x1) * dy / dx;
+		x = 0;
+		draw_vertical_line(raster, 0, y1, y, ydir);
+		x1 = x;
+		y1 = y;
+	} else if (x2 < 0 && x1 >= 0) {
+		y = y1 + (0 - x1) * dy / dx;
+		x = 0;
+		draw_vertical_line(raster, 0, y, y2, ydir);
+		x2 = x;
+		y2 = y;
+	}
+	if (x1 < w && x2 >= w) {
+		y = y1 + (w - x1) * dy / dx;
+		x = w;
+		draw_vertical_line_opposite_only(raster, raster->width - 1, y, y2, ydir);
+		x2 = x;
+		y2 = y;
+	} else if (x2 < w && x1 >= w) {
+		y = y1 + (w - x1) * dy / dx;
+		x = w;
+		draw_vertical_line_opposite_only(raster, raster->width - 1, y1, y, ydir);
+		x1 = x;
+		y1 = y;
+	}
+
+	/* Now we can finally draw the part of the
+	 * line that is inside the raster */
+	if (!xdir) {
+		/* Optimisation for vertical lines. It also serves
+		 * to illustrate how the algorithm is designed. */
+		draw_vertical_line(raster, x1, y1, y2, ydir);
+	} else {
+		draw_diagonal_line(raster, x1, y1, x2, y2, dx, dy, xdir, ydir);
+	}
+}
+
+
+#else
+
+
+int
+main(void)
+{
+	return 0; /* TODO add test */
+}
+
+
+#endif