From: Ben Harris <bjh21@bjh21.me.uk>
Date: Mon, 21 Oct 2024 08:31:57 +0000 (+0100)
Subject: Make co-ordinate systems more sensible
X-Git-Tag: bedstead-3.246~105
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~bjharris/git?a=commitdiff_plain;h=32079c7b7547fa4ba5921070a92501576696aee3;p=bedstead.git

Make co-ordinate systems more sensible

The SAA5050 character images appear at the bottom-right corner of the
character cell, with a blank pixel to the top and the left.  This can
be seen if you put am alphanumeric character and a mosaic graphics
character side-by-side, since mosaic graphics characters fill the
entire character cell.

However, when I first made Bedstead, I put the character images in the
top-right corner, and the co-ordinate system matched that.  When I
fixed this in 2013 (commit 7bea0c6fadc35de50ea08eb184d4b15a7b411ef3),
I just did it by adjusting the final transformation of the vector
co-ordinates, leaving all the internal co-ordinate systems intact.
This was visible when I added mosaic graphics, which had to be offset
by one pixel to compensate.

Now I've finally corrected the problem somewhat properly.  Pixel
co-ordinates count from (0,0) in the top-left corner of the character
cell.  Vector co-ordinates count from (0,0) in the bottom-left corner
and are offset to the baseline on emission.  The conversion between
the two forms is still weirdly spread all over the place though.
---

diff --git a/bedstead.c b/bedstead.c
index 6759768..65c1c11 100644
--- a/bedstead.c
+++ b/bedstead.c
@@ -198,7 +198,8 @@ static void glyph_complement(void);
 
 static struct glyph {
 	union {
-		char data[YSIZE];
+		/* Top row (and left column) don't appear in ROM. */
+		char data[YSIZE - 1];
 		char const *alias_of;
 	};
 	int_least32_t unicode;
@@ -2620,10 +2621,17 @@ static bool
 getpix(char const data[YSIZE], int x, int y, unsigned flags)
 {
 
-	if (x < 0 || x >= XSIZE || y < 0 || y >= YSIZE)
+	/*
+	 * Pixel co-ordinates count from (0,0) in the top left of the
+	 * character cell.  In the glyph array, the top row isn't
+	 * represented and the columns are right-aligned in a char.
+	 * Like the top row, the left column of the character cell
+	 * always reads as 0.
+	 */
+	if (x < 1 || x >= XSIZE || y < 1 || y >= YSIZE)
 		return 0;
 	else
-		return (data[y] >> (XSIZE - x - 1)) & 1;
+		return (data[y - 1] >> (XSIZE - x - 1)) & 1;
 }
 
 static bool plottermode = false;
@@ -3349,7 +3357,7 @@ emit_contour(point *p0)
 	do {
 		printf(" %g %g %s 1\n",
 		       (double)p->v.x / XSCALE,
-		       (double)p->v.y / YSCALE - 3*YPIX,
+		       (double)p->v.y / YSCALE - 2*YPIX,
 		       p == p0 && p->next ? "m" : "l");
 		p1 = p->next;
 		p->prev = p->next = NULL;
@@ -3684,12 +3692,12 @@ domosaic(unsigned code, bool sep)
 {
 
 	clearpath();
-	if (code & 1)  tile(0 + sep, 8 + sep, 3, 11);
-	if (code & 2)  tile(3 + sep, 8 + sep, 6, 11);
-	if (code & 4)  tile(0 + sep, 4 + sep, 3, 8);
-	if (code & 8)  tile(3 + sep, 4 + sep, 6, 8);
-	if (code & 16) tile(0 + sep, 1 + sep, 3, 4);
-	if (code & 32) tile(3 + sep, 1 + sep, 6, 4);
+	if (code & 1)  tile(0 + sep, 7 + sep, 3, 10);
+	if (code & 2)  tile(3 + sep, 7 + sep, 6, 10);
+	if (code & 4)  tile(0 + sep, 3 + sep, 3, 7);
+	if (code & 8)  tile(3 + sep, 3 + sep, 6, 7);
+	if (code & 16) tile(0 + sep, 0 + sep, 3, 3);
+	if (code & 32) tile(3 + sep, 0 + sep, 6, 3);
 	clean_path();
 	emit_path();
 }
@@ -3699,10 +3707,10 @@ domosaic4(unsigned code, bool sep)
 {
 
 	clearpath();
-	if (code & 1) tile(0 + sep, 6 + sep, 3, 11);
-	if (code & 2) tile(3 + sep, 6 + sep, 6, 11);
-	if (code & 4) tile(0 + sep, 1 + sep, 3, 6);
-	if (code & 8) tile(3 + sep, 1 + sep, 6, 6);
+	if (code & 1) tile(0 + sep, 5 + sep, 3, 10);
+	if (code & 2) tile(3 + sep, 5 + sep, 6, 10);
+	if (code & 4) tile(0 + sep, 0 + sep, 3, 5);
+	if (code & 8) tile(3 + sep, 0 + sep, 6, 5);
 	clean_path();
 	emit_path();
 }