add error texture

src/app.zig

@@ -69,7 +69,7 @@ pub fn frame(self: *App, plt: Platform.Frame) !void {
 
     Gfx.setClearColor(self.bg);
     Gfx.drawTexture(self.tex, self.player_pos, .init(100, 100), .rgb(200, 0, 0));
-    Gfx.drawRectangle(self.player_pos.add(.init(0, 200)), .init(100, 100), .rgb(200, 200, 0));
+    Gfx.drawRectangle(self.player_pos.add(.init(0, 200)), .init(100, 100), .rgb(255, 255, 255));
 
     if (ImGUI.beginWindow(.{
         .name = "Hello",

src/color.zig

@@ -10,6 +10,7 @@ a: f32,
 
 pub const black = rgb(0, 0, 0);
 pub const white = rgb(255, 255, 255);
+pub const purple = rgb(255, 0, 255);
 
 pub fn rgba(r: u8, g: u8, b: u8, a: f32) Color {
     assert(0 <= a and a <= 1);

src/graphics.zig

@@ -24,6 +24,7 @@ const State = struct {
     bindings: sg.Bindings,
 
     default_texture: TextureId,
+    error_texture: TextureId,
     default_sampler: sg.Sampler,
 
     quads_buffer: [2048]Quad,
@@ -129,7 +130,8 @@ pub fn init(gpa: std.mem.Allocator, logger: sg.Logger) !void {
         .clear_color = .black,
         .textures_buffer = undefined,
         .textures_slotmap = .init(try .initCapacity(gpa, max_textures)),
-        .default_texture = undefined
+        .default_texture = undefined,
+        .error_texture = undefined
     };
 
     {
@@ -142,6 +144,34 @@ pub fn init(gpa: std.mem.Allocator, logger: sg.Logger) !void {
         self.default_texture = try initTexture();
         try setTexture(self.default_texture, &pixels, width, height);
     }
+
+    {
+        const width = 8;
+        const height = 8;
+
+        var pixels: [width * height * 4]u8 = undefined;
+        for (0..height) |y| {
+            for (0..width) |x| {
+                const pixel_index = y * width + x;
+
+                var color: Color = undefined;
+                if ((pixel_index+y) % 2 == 0) {
+                    color = .purple;
+                } else {
+                    color = .black;
+                }
+
+                const pixel = pixels[(4*pixel_index)..];
+                pixel[0] = @intFromFloat(color.r*255);
+                pixel[1] = @intFromFloat(color.g*255);
+                pixel[2] = @intFromFloat(color.b*255);
+                pixel[3] = @intFromFloat(color.a*255);
+            }
+        }
+
+        self.error_texture = try initTexture();
+        try setTexture(self.error_texture, &pixels, width, height);
+    }
 }
 
 pub fn deinit() void {
@@ -306,7 +336,8 @@ pub fn deinitTexture(id: TextureId) void {
         const texture = self.textures_buffer[id.index];
         const bound_view = &self.bindings.views[shd.VIEW_tex];
         if (texture.view.id == bound_view.id) {
-            bound_view.* = self.default_view;
+            assert(self.textures_slotmap.exists(self.default_texture));
+            bound_view.* = self.textures_buffer[self.default_texture.index].view;
         }
 
         sg.destroyView(texture.view);
@@ -366,24 +397,27 @@ const DrawOptions = struct {
 
 pub fn draw(opts: DrawOptions) void {
     const self = &g_state;
-    if (!self.textures_slotmap.exists(opts.texture)) {
-        // TODO: Draw purple-black texture
-        return;
+
+    var quad = opts.quad;
+    var texture = opts.texture;
+    if (!self.textures_slotmap.exists(texture)) {
+        texture = self.error_texture;
+        quad.setColor(.white);
     }
 
-    const texture = self.textures_buffer[opts.texture.index];
+    const view = self.textures_buffer[texture.index].view;
 
     const bound_view = &self.bindings.views[shd.VIEW_tex];
-    if (bound_view.id != texture.view.id) {
+    if (bound_view.id != view.id) {
         flush();
-        bound_view.* = texture.view;
+        bound_view.* = view;
     }
 
     if (self.quads.items.len == self.quads.capacity) {
         flush();
     }
 
-    self.quads.appendAssumeCapacity(opts.quad);
+    self.quads.appendAssumeCapacity(quad);
 }
 
 const Texture = struct {