From 4adb0cfda7fdff997f5ef552354eea6745e85c2b Mon Sep 17 00:00:00 2001
From: Alex Bethel <abethel@cs.nmt.edu>
Date: Mon, 29 Nov 2021 17:16:25 -0700
Subject: [PATCH] Fix #1

---
 src/graphics_api_impl.rs | 69 ++++++++++++++++++++++++++++++----------
 src/main.rs              |  4 +--
 2 files changed, 55 insertions(+), 18 deletions(-)

diff --git a/src/graphics_api_impl.rs b/src/graphics_api_impl.rs
index f0f07e9..8ce7196 100644
--- a/src/graphics_api_impl.rs
+++ b/src/graphics_api_impl.rs
@@ -1,6 +1,6 @@
 #![allow(dead_code, unused)]
 
-use ab_glyph::FontRef;
+use ab_glyph::{FontRef, ScaleFont};
 use able_graphics_library::{AglApi, FrameBuffer, Point, HEIGHT, RGBA, WIDTH};
 use mini_gl_fb::glutin::platform::unix::x11::ffi::XK_R10;
 
@@ -78,25 +78,50 @@ impl AglApi for GraphicsRenderer {
     fn draw_text(&mut self, coords: Point, scale: u8, color: RGBA, text: String) {
         use ab_glyph::{point, Font, FontRef, Glyph};
 
-        let font: FontRef =
-            FontRef::try_from_slice(include_bytes!("../font/Roboto-Regular.ttf")).unwrap();
+        let font = FontRef::try_from_slice(include_bytes!("../font/Roboto-Regular.ttf")).unwrap();
+        let font_scaled = font.as_scaled(scale as f32);
 
-        // Get a glyph for 'q' with a scale & position.
-        let q_glyph: Glyph = font
-            .glyph_id('a')
-            .with_scale_and_position(scale as f32, point(coords.x as f32, coords.y as f32));
-        // Draw it.
-        if let Some(q) = font.outline_glyph(q_glyph) {
-            // dbg!(q);
+        // Individual characters are drawn at floating-point offsets.
+        let mut coords = point(coords.x as f32, coords.y as f32);
+        let mut last_char = None;
 
-            q.draw(|x, y, c| {
-                /* draw pixel `(x, y)` with coverage: `c` */
-                dbg!(x, y, c);
+        for ch in text.chars() {
+            let glyph_id = font.glyph_id(ch);
 
-                let coordinates = x as u16 + (WIDTH as u16).wrapping_mul(y as u16);
+            // Kern character pairs as necessary.
+            if let Some(last) = last_char {
+                coords.x -= font_scaled.kern(last, glyph_id);
+            }
+            last_char = Some(font.glyph_id(ch));
 
-                self.buff[coordinates as usize] = color;
-            });
+            // Get a glyph with a scale & position.
+            let glyph: Glyph = glyph_id
+                .with_scale_and_position(scale as f32, point(coords.x as f32, coords.y as f32));
+
+            // Draw it.
+            if let Some(outline) = font.outline_glyph(glyph) {
+                outline.draw(|x, y, c| {
+                    // ab_glyph gives us coordinates within the
+                    // bounding box; convert these to coordinates
+                    // within the image.
+                    let corner = outline.px_bounds().min;
+                    let (x, y) = (x + corner.x as u32, y + corner.y as u32);
+
+                    // Flip y to draw characters right-side-up.
+                    let y = 2 * coords.y as u32 - y;
+
+                    // draw pixel `(x, y)` with coverage: `c`
+                    let coordinates = x as u16 + (WIDTH as u16).wrapping_mul(y as u16);
+                    let pixel = &mut self.buff[coordinates as usize];
+
+                    // Interpolate between the existing background
+                    // character and the new foreground color.
+                    *pixel = lerp_rgba(*pixel, color, c);
+                });
+            }
+
+            // Advance to the next glyph's position.
+            coords.x += font_scaled.h_advance(glyph_id);
         }
     }
     /// Actually move the double buffer to the single buffer and "update" the screen
@@ -107,3 +132,15 @@ impl AglApi for GraphicsRenderer {
         }
     }
 }
+
+/// Interpolate between two colors according to a factor.
+fn lerp_rgba(a: RGBA, b: RGBA, fac: f32) -> RGBA {
+    // TODO: This is probably the wrong way to mix colors, but it's
+    // simple and works for now.
+    RGBA {
+        r: ((b.r as f32 - a.r as f32) * fac + a.r as f32) as _,
+        g: ((b.g as f32 - a.g as f32) * fac + a.g as f32) as _,
+        b: ((b.b as f32 - a.b as f32) * fac + a.b as f32) as _,
+        a: ((b.a as f32 - a.a as f32) * fac + a.a as f32) as _,
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index 0bda1e5..6a3187f 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -73,8 +73,8 @@ fn main() {
     );
 
     xyz.draw_text(
-        Point { x: 1000, y: 90 },
-        1,
+        Point { x: 100, y: 90 },
+        24,
         RGBA {
             r: 0,
             g: 0,