From 9e97d9b80dbe0786fedfa46942bd9308a47bc9be Mon Sep 17 00:00:00 2001
From: cflip <cflip@cflip.net>
Date: Thu, 12 Jan 2023 14:14:17 -0700
Subject: Big improvements to font rendering

The previous rasterizing code relied on each row in the font being 8
bits wide, which is not the case with any font wider than 8 pixels.
These changes make it possible to properly load the 24px Terminus font,
and somehow also fixes incorrect characters in the 12px font.
---
 font.c   | 10 ++++++----
 window.c |  4 ++--
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/font.c b/font.c
index c1d1e7a..d0d3f72 100644
--- a/font.c
+++ b/font.c
@@ -9,8 +9,8 @@ SDL_Texture *font_create_texture(SDL_Renderer *renderer, PSFFont *font)
 {
 	SDL_Texture *result;
 
+	const int bytes_per_row = (font->bytes_per_glyph / font->height);
 	const int texture_width = font->num_glyphs * font->width;
-	const int bits_per_glyph = 8;
 	SDL_Surface *surface = SDL_CreateRGBSurface(0, texture_width, font->height, 32, 0, 0, 0, 0);
 
 	for (int glyph_idx = 0; glyph_idx < font->num_glyphs; glyph_idx++) {
@@ -20,11 +20,12 @@ SDL_Texture *font_create_texture(SDL_Renderer *renderer, PSFFont *font)
 				 * TODO: Make it possible for the texture atlas to have more
 				 * than one row.
 				 */
-				int xp = x + glyph_idx * bits_per_glyph;
+				int xp = x + glyph_idx * font->width;
 				int yp = y;
 
-				int bit_idx = 8 - 1 - x;
-				char current_bit = font->glyph_data[glyph_idx * font->bytes_per_glyph + y] & (1 << bit_idx);
+				int bit_idx = 7 - (x % 8);
+				int row_byte_idx = (glyph_idx * font->bytes_per_glyph) + y * bytes_per_row + (x / 8);
+				char current_bit = font->glyph_data[row_byte_idx] & (1 << bit_idx);
 				((Uint32*)(surface->pixels))[xp + yp * surface->w] = current_bit ? 0xffffffff : 0;
 			}
 		}
@@ -64,6 +65,7 @@ PSFFont font_load(const char *filename)
 
 	size_t glyph_buffer_size = font.num_glyphs * font.bytes_per_glyph;
 	font.glyph_data = malloc(glyph_buffer_size);
+	fseek(fp, font.header_size, SEEK_SET);
 	fread(font.glyph_data, font.bytes_per_glyph, font.num_glyphs, fp);
 
 	font.unicode_desc = NULL;
diff --git a/window.c b/window.c
index 1c300b7..3ffd748 100644
--- a/window.c
+++ b/window.c
@@ -19,7 +19,7 @@ void window_init(const char *title, int rows, int cols)
 	if (SDL_Init(SDL_INIT_VIDEO) != 0)
 		fatal_error("Failed to init SDL: %s\n", SDL_GetError());
 
-	font = font_load("terminus/ter-u12n.psf");
+	font = font_load("terminus/ter-u24n.psf");
 	int window_width = cols * font.width;
 	int window_height = rows * font.height;
 
@@ -82,7 +82,7 @@ static void draw_font_text(struct append_buffer *buffer)
 		dstrect.w = font.width;
 		dstrect.h = font.height;
 
-		srcrect.x = glyph_index * 8;
+		srcrect.x = glyph_index * font.width;
 		srcrect.y = 0;
 		srcrect.w = font.width;
 		srcrect.h = font.height;
-- 
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