Blitter: Change DrawLine to be templated

src/blitter/base.hpp

@@ -14,6 +14,7 @@
 
 #include "../spritecache.h"
 #include "../spriteloader/spriteloader.hpp"
+#include "../core/math_func.hpp"
 
 /** The modes of blitting we can do. */
 enum BlitterMode {
@@ -142,7 +143,7 @@ public:
 	 * @param width Line width.
 	 * @param dash Length of dashes for dashed lines. 0 means solid line.
 	 */
-	virtual void DrawLine(void *video, int x, int y, int x2, int y2, int screen_width, int screen_height, uint8 colour, int width, int dash = 0);
+	virtual void DrawLine(void *video, int x, int y, int x2, int y2, int screen_width, int screen_height, uint8 colour, int width, int dash = 0) = 0;
 
 	/**
 	 * Copy from a buffer to the screen.
@@ -223,6 +224,131 @@ public:
 	virtual void PostResize() { };
 
 	virtual ~Blitter() { }
+
+	template <typename SetPixelT> void DrawLineGeneric(int x, int y, int x2, int y2, int screen_width, int screen_height, int width, int dash, SetPixelT set_pixel);
 };
 
+template <typename SetPixelT>
+void Blitter::DrawLineGeneric(int x, int y, int x2, int y2, int screen_width, int screen_height, int width, int dash, SetPixelT set_pixel)
+{
+	int dy;
+	int dx;
+	int stepx;
+	int stepy;
+
+	dy = (y2 - y) * 2;
+	if (dy < 0) {
+		dy = -dy;
+		stepy = -1;
+	} else {
+		stepy = 1;
+	}
+
+	dx = (x2 - x) * 2;
+	if (dx < 0) {
+		dx = -dx;
+		stepx = -1;
+	} else {
+		stepx = 1;
+	}
+
+	if (dx == 0 && dy == 0) {
+		/* The algorithm below cannot handle this special case; make it work at least for line width 1 */
+		if (x >= 0 && x < screen_width && y >= 0 && y < screen_height) set_pixel(x, y);
+		return;
+	}
+
+	int frac_diff = width * max(dx, dy);
+	if (width > 1) {
+		/* compute frac_diff = width * sqrt(dx*dx + dy*dy)
+		 * Start interval:
+		 *    max(dx, dy) <= sqrt(dx*dx + dy*dy) <= sqrt(2) * max(dx, dy) <= 3/2 * max(dx, dy) */
+		int frac_sq = width * width * (dx * dx + dy * dy);
+		int frac_max = 3 * frac_diff / 2;
+		while (frac_diff < frac_max) {
+			int frac_test = (frac_diff + frac_max) / 2;
+			if (frac_test * frac_test < frac_sq) {
+				frac_diff = frac_test + 1;
+			} else {
+				frac_max = frac_test - 1;
+			}
+		}
+	}
+
+	int gap = dash;
+	if (dash == 0) dash = 1;
+	int dash_count = 0;
+	if (dx > dy) {
+		int y_low     = y;
+		int y_high    = y;
+		int frac_low  = dy - frac_diff / 2;
+		int frac_high = dy + frac_diff / 2;
+
+		while (frac_low + dx / 2 < 0) {
+			frac_low += dx;
+			y_low -= stepy;
+		}
+		while (frac_high - dx / 2 >= 0) {
+			frac_high -= dx;
+			y_high += stepy;
+		}
+		x2 += stepx;
+
+		while (x != x2) {
+			if (dash_count < dash && x >= 0 && x < screen_width) {
+				for (int y = y_low; y != y_high; y += stepy) {
+					if (y >= 0 && y < screen_height) set_pixel(x, y);
+				}
+			}
+			if (frac_low >= 0) {
+				y_low += stepy;
+				frac_low -= dx;
+			}
+			if (frac_high >= 0) {
+				y_high += stepy;
+				frac_high -= dx;
+			}
+			x += stepx;
+			frac_low += dy;
+			frac_high += dy;
+			if (++dash_count >= dash + gap) dash_count = 0;
+		}
+	} else {
+		int x_low     = x;
+		int x_high    = x;
+		int frac_low  = dx - frac_diff / 2;
+		int frac_high = dx + frac_diff / 2;
+
+		while (frac_low + dy / 2 < 0) {
+			frac_low += dy;
+			x_low -= stepx;
+		}
+		while (frac_high - dy / 2 >= 0) {
+			frac_high -= dy;
+			x_high += stepx;
+		}
+		y2 += stepy;
+
+		while (y != y2) {
+			if (dash_count < dash && y >= 0 && y < screen_height) {
+				for (int x = x_low; x != x_high; x += stepx) {
+					if (x >= 0 && x < screen_width) set_pixel(x, y);
+				}
+			}
+			if (frac_low >= 0) {
+				x_low += stepx;
+				frac_low -= dy;
+			}
+			if (frac_high >= 0) {
+				x_high += stepx;
+				frac_high -= dy;
+			}
+			y += stepy;
+			frac_low += dx;
+			frac_high += dx;
+			if (++dash_count >= dash + gap) dash_count = 0;
+		}
+	}
+}
+
 #endif /* BLITTER_BASE_HPP */