Generate no_tile.png

img/no_tile.py

+#!/usr/bin/python3
+
+import cairo
+import math
+
+img = cairo.ImageSurface(cairo.FORMAT_ARGB32, 256, 256)
+cx = cairo.Context(img)
+cx.set_source_rgb(0.125, 0.125, 0.125)
+cx.paint()
+
+cx.set_source_rgb(0.25, 0.25, 0.25)
+
+for i in range(1, 8):
+    num = 2 ** i
+    for j in range(0, num + 1):
+        x = float(j) * 256.0 / num
+        w = 8.0 / num
+        cx.rectangle(x - w * 0.5, 0, w, 256)
+        cx.rectangle(0, x - w * 0.5, 256, w)
+
+cx.fill()
+
+img.write_to_png('no_tile.png')

src/map_view_gl.rs

             let mut tex = Texture::empty(cx, 2048, 2048, TextureFormat::Rgb8);
             check_gl_errors!(cx);
             {
-                let img = image::open("no_tile.png").unwrap();
+                let img = image::open("img/no_tile.png").unwrap();
                 tex.sub_image(0, 0, &img);
                 check_gl_errors!(cx);
             }