From eac7a1fef3b07a73efe4239c8f043c0b5dd822cb Mon Sep 17 00:00:00 2001
From: Mattias Andrée <maandree@kth.se>
Date: Sun, 5 Feb 2023 11:21:28 +0100
Subject: Add draw_linear_bezier_reference
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Signed-off-by: Mattias Andrée <maandree@kth.se>
---
 draw_linear_bezier_reference.c | 111 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 draw_linear_bezier_reference.c

(limited to 'draw_linear_bezier_reference.c')

diff --git a/draw_linear_bezier_reference.c b/draw_linear_bezier_reference.c
new file mode 100644
index 0000000..6066946
--- /dev/null
+++ b/draw_linear_bezier_reference.c
@@ -0,0 +1,111 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+#ifndef TEST
+
+/*
+ * The implementation in this fill is not supposed to be fast,
+ * it is supposed to be absolutely correct. The implementation
+ * shall be as clear and obvious as possible. It is important
+ * that everything written to cells is as precise as possible
+ * and that the function behavious correctly when outside the
+ * raster. This implementation shall be usable to generate an
+ * as perfect as possible rasterisation and shall be usable to
+ * test the correctness and accuracy of the fast implementation.
+ */
+
+
+void
+draw_linear_bezier_reference(RASTER *restrict raster, double x1, double y1, double x2, double y2)
+{
+	double dx = x2 - x1;
+	double dy = y2 - y1;
+	int xdir = SIGNUM(dx);
+	int ydir = SIGNUM(dy);
+	double kx = dx / dy;
+	double ky = dy / dx;
+	double prevX, prevY, x, y, cx, cy, h2x, h2y;
+	double xfloor, yfloor;
+	ssize_t cellX, cellY;
+	size_t cell;
+
+	prevX = x1;
+	prevY = y1;
+
+	for (; prevX != x2 && prevY != y2; prevX = x, prevY = y) {
+		/* Find next vertical and next hozitonal grid line */
+		x = xdir < 0 ? floor(prevX) : xdir > 0 ? ceil(prevX) : prevX;
+		y = ydir < 0 ? floor(prevY) : ydir > 0 ? ceil(prevY) : prevY;
+		x = x == prevX ? x + xdir : x;
+		y = y == prevY ? y + ydir : y;
+
+		/* Limit to the extend of the drawn line segment */
+		if ((xdir < 0 && x < x2) || (xdir > 0 && x > x2))
+			x = x2;
+		if ((ydir < 0 && y < y2) || (ydir > 0 && y > y2))
+			y = y2;
+
+		/* Find next cell edge */
+		if (xdir && ydir) {
+			cy = y1 + (x - x1) * ky;
+			cx = x1 + (y - y1) * kx;
+			h2x = (cy - prevY) * (cy - prevY) + (x - prevX) * (x - prevX);
+			h2y = (cx - prevX) * (cx - prevX) + (y - prevY) * (y - prevY);
+			if (h2x < h2y)
+				y = cy;
+			else
+				x = cx;
+
+			/* Make sure loop will exit when we reach the end */
+			if ((xdir < 0 && x < x2) || (xdir > 0 && x > x2))
+				x = x2;
+			if ((ydir < 0 && y < y2) || (ydir > 0 && y > y2))
+				y = y2;
+		}
+
+		/* Select cell to draw in */
+		xfloor = xdir >= 0 ? floor(prevX) : floor(x);
+		yfloor = ydir >= 0 ? floor(prevY) : floor(y);
+		cellX = (ssize_t)xfloor;
+		cellY = (ssize_t)yfloor;
+
+		/* Do not draw if above or below the raster*/
+		if (cellY < 0 || (size_t)cellY >= raster->height)
+			continue;
+
+		if (cellX < 0) {
+			/* Draw on first column in raster of outside of raster on the left side,
+			 * with full horizontal coverage, `.opposite_coverage` one the actual
+			 * cell (outside of the raster) will contribute to the first column's
+			 * `.cell_coverage` */
+			cell = (size_t)cellY * raster->width;
+			raster->cells[cell].opposite_coverage += y - prevY;
+			raster->cells[cell].cell_coverage += y - prevY;
+
+		} else if ((size_t)cellX >= raster->width) {
+			/* If outside of the raster, on the right side, add to the last
+			 * columns contributions to the next column, so that the ink level
+			 * balances out to zero */
+			cell = (size_t)cellY * raster->width + (raster->width - 1);
+			raster->cells[cell].opposite_coverage += y - prevY;
+
+		} else {
+			/* If inside the raster, just draw the line */
+			cell = (size_t)cellY * raster->width + (size_t)cellX;
+			raster->cells[cell].opposite_coverage += y - prevY;
+			raster->cells[cell].cell_coverage += (y - prevY) * fabs(fmax(ceil(x), ceil(prevX)) - (x + prevX) / 2.0);
+		}
+	}
+}
+
+
+#else
+
+
+int
+main(void)
+{
+	return 0; /* TODO add test */
+}
+
+
+#endif
-- 
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