From 7a00c54f25d0a0946ab0a7564e63ee63750c1a5e Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Tue, 19 Apr 2022 09:20:55 -0700
Subject: [PATCH] cell: convert atlas x/y to NDC in shader

---
 shaders/cell.v.glsl |  8 +++++---
 src/FontAtlas.zig   | 15 ++++++---------
 src/Grid.zig        | 12 ++++++------
 3 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/shaders/cell.v.glsl b/shaders/cell.v.glsl
index 722d2ec20..d6eb693d9 100644
--- a/shaders/cell.v.glsl
+++ b/shaders/cell.v.glsl
@@ -71,10 +71,12 @@ void main() {
         cell_pos = cell_pos + glyph_size * position + glyph_offset_calc;
         gl_Position = projection * vec4(cell_pos, 0.0, 1.0);
 
-        // Calculate our texture coordinate
+        // We need to convert our texture position and size to normalized
+        // device coordinates (0 to 1.0) by dividing by the size of the texture.
         ivec2 text_size = textureSize(text, 0);
-        vec2 glyph_tex_size = glyph_size / text_size.xy;
-        glyph_tex_coords = glyph_pos + glyph_tex_size * position;
+        vec2 glyph_tex_pos = glyph_pos / text_size;
+        vec2 glyph_tex_size = glyph_size / text_size;
+        glyph_tex_coords = glyph_tex_pos + glyph_tex_size * position;
 
         // Set our foreground color output
         color = fg_color_in / 255.;
diff --git a/src/FontAtlas.zig b/src/FontAtlas.zig
index fdf6f691f..87680bafc 100644
--- a/src/FontAtlas.zig
+++ b/src/FontAtlas.zig
@@ -41,11 +41,10 @@ pub const Glyph = struct {
     /// top bearing
     offset_y: i32,
 
-    /// normalized x, y (s, t) coordinates
-    s0: f32,
-    t0: f32,
-    s1: f32,
-    t1: f32,
+    /// coordinates in the atlas of the top-left corner. These have to
+    /// be normalized to be between 0 and 1 prior to use.
+    atlas_x: u32,
+    atlas_y: u32,
 
     /// horizontal position to increase drawing position for strings
     advance_x: f32,
@@ -170,10 +169,8 @@ pub fn addGlyph(self: *FontAtlas, alloc: Allocator, v: anytype) !*Glyph {
         .height = tgt_h,
         .offset_x = glyph.*.bitmap_left,
         .offset_y = glyph.*.bitmap_top,
-        .s0 = @intToFloat(f32, region.x) / @intToFloat(f32, self.atlas.size),
-        .t0 = @intToFloat(f32, region.y) / @intToFloat(f32, self.atlas.size),
-        .s1 = @intToFloat(f32, region.x + tgt_w) / @intToFloat(f32, self.atlas.size),
-        .t1 = @intToFloat(f32, region.y + tgt_h) / @intToFloat(f32, self.atlas.size),
+        .atlas_x = region.x,
+        .atlas_y = region.y,
         .advance_x = f26dot6ToFloat(glyph.*.advance.x),
     };
 
diff --git a/src/Grid.zig b/src/Grid.zig
index 14e84001a..93a677633 100644
--- a/src/Grid.zig
+++ b/src/Grid.zig
@@ -41,8 +41,8 @@ const GPUCell = struct {
     grid_row: u16,
 
     /// vec2 glyph_pos
-    glyph_x: f32,
-    glyph_y: f32,
+    glyph_x: u32,
+    glyph_y: u32,
 
     /// vec2 glyph_size
     glyph_width: u32,
@@ -139,8 +139,8 @@ pub fn init(alloc: Allocator) !Grid {
     var offset: usize = 0;
     try vbobind.attributeAdvanced(0, 2, gl.c.GL_UNSIGNED_SHORT, false, @sizeOf(GPUCell), offset);
     offset += 2 * @sizeOf(u16);
-    try vbobind.attributeAdvanced(1, 2, gl.c.GL_FLOAT, false, @sizeOf(GPUCell), offset);
-    offset += 2 * @sizeOf(f32);
+    try vbobind.attributeAdvanced(1, 2, gl.c.GL_UNSIGNED_INT, false, @sizeOf(GPUCell), offset);
+    offset += 2 * @sizeOf(u32);
     try vbobind.attributeAdvanced(2, 2, gl.c.GL_UNSIGNED_INT, false, @sizeOf(GPUCell), offset);
     offset += 2 * @sizeOf(u32);
     try vbobind.attributeAdvanced(3, 2, gl.c.GL_INT, false, @sizeOf(GPUCell), offset);
@@ -251,8 +251,8 @@ pub fn updateCells(self: *Grid, term: Terminal) !void {
             self.cells.appendAssumeCapacity(.{
                 .grid_col = @intCast(u16, x),
                 .grid_row = @intCast(u16, y),
-                .glyph_x = glyph.s0,
-                .glyph_y = glyph.t0,
+                .glyph_x = glyph.atlas_x,
+                .glyph_y = glyph.atlas_y,
                 .glyph_width = glyph.width,
                 .glyph_height = glyph.height,
                 .glyph_offset_x = glyph.offset_x,