add gradient at bottom

src/app.zig

@@ -43,6 +43,7 @@ font: Gfx.Font.Id,
 idle_animations: AnimationDirections,
 walk_animations: AnimationDirections,
 death_animations: AnimationDirections,
+gradient_sprite: Gfx.Sprite.Id,
 
 terrain_sheet: Tilesheet,
 terrain_tiles: []Tile,
@@ -473,6 +474,23 @@ pub fn init(self: *App, plt: Platform.Init) !?u8 {
 
     const now = std.Io.Timestamp.now(plt.io, .awake);
 
+    var gradient_sprite = Gfx.getNilSprite();
+    {
+        var gradient_data = try Gfx.ImageData.init(plt.gpa, 1, 32, .rgba8);
+        defer gradient_data.deinit(plt.gpa);
+        for (0..gradient_data.height) |y| {
+            const percent = @as(f32, @floatFromInt(y)) / @as(f32, @floatFromInt(gradient_data.height));
+            const pixel = gradient_data.getPixel(0, @intCast(y));
+            pixel[0] = 0;
+            pixel[1] = 0;
+            pixel[2] = 0;
+            pixel[3] = @intFromFloat(percent*255);
+        }
+
+        gradient_sprite = Gfx.initSprite(.{});
+        Gfx.setSprite(gradient_sprite, .{ .image = gradient_data });
+    }
+
     self.* = App{
         .gpa = plt.gpa,
         .idle_animations = try AnimationDirections.init(plt.arena, idle_sheet, ns_per_s / idle_fps, 2),
@@ -486,6 +504,7 @@ pub fn init(self: *App, plt: Platform.Init) !?u8 {
         .eternal_flame_id = undefined,
         .upgrades = .{},
         .shop = undefined,
+        .gradient_sprite = gradient_sprite,
 
         .terrain_sheet = terrain_sheet,
         .terrain_tiles = terrain_tiles,
@@ -1848,6 +1867,8 @@ pub fn frame(self: *App, plt: Platform.Frame) !void {
                 Gfx.drawSprite(tile.sprite, tile_pos.multiply(terrain_tile_size), terrain_tile_size, .white);
             }
         }
+
+        Gfx.drawSprite(self.gradient_sprite, .init(-2500, 64), .init(5000, 96), .white);
     }
 
     {

src/graphics.zig

@@ -1711,7 +1711,7 @@ pub const ImageData = struct {
         }
     }
 
-    fn getPixel(self: ImageData, x: u32, y: u32) []u8 {
+    pub fn getPixel(self: ImageData, x: u32, y: u32) []u8 {
         const pixel_index = y * self.width + x;
         if (self.pixels) |pixels| {
             return switch (pixels) {