Merge pull request #2033 from lightpanda-io/canvas_context_cache

Canvas context cache

Author: karlseguin

src/browser/tests/canvas/canvas_rendering_context_2d.html

@@ -148,3 +148,13 @@
 
 }
 </script>
+
+<script id=identity>
+{
+  const element = document.createElement('canvas');
+  const ctx = element.getContext('2d');
+
+  testing.expectTrue(ctx === element.getContext('2d'));
+  testing.expectEqual(null, element.getContext('webgl'));
+}
+</script>

src/browser/tests/canvas/webgl_rendering_context.html

@@ -85,3 +85,13 @@
   loseContext.restoreContext();
 }
 </script>
+
+<script id=identity>
+{
+  const element = document.createElement('canvas');
+  const ctx = element.getContext('webgl');
+
+  testing.expectTrue(ctx === element.getContext('webgl'));
+  testing.expectEqual(null, element.getContext('2d'));
+}
+</script>

src/browser/webapi/element/html/Canvas.zig

@@ -29,6 +29,9 @@ const OffscreenCanvas = @import("../../canvas/OffscreenCanvas.zig");
 
 const Canvas = @This();
 _proto: *HtmlElement,
+_cached: ?DrawingContext = null,
+
+const ContextType = enum { none, @"2d", webgl };
 
 pub fn asElement(self: *Canvas) *Element {
     return self._proto._proto;
@@ -68,17 +71,28 @@ const DrawingContext = union(enum) {
 };
 
 pub fn getContext(self: *Canvas, context_type: []const u8, page: *Page) !?DrawingContext {
-    if (std.mem.eql(u8, context_type, "2d")) {
-        const ctx = try page._factory.create(CanvasRenderingContext2D{ ._canvas = self });
-        return .{ .@"2d" = ctx };
-    }
-
-    if (std.mem.eql(u8, context_type, "webgl") or std.mem.eql(u8, context_type, "experimental-webgl")) {
-        const ctx = try page._factory.create(WebGLRenderingContext{});
-        return .{ .webgl = ctx };
+    if (self._cached) |cached| {
+        const matches = switch (cached) {
+            .@"2d" => std.mem.eql(u8, context_type, "2d"),
+            .webgl => std.mem.eql(u8, context_type, "webgl") or std.mem.eql(u8, context_type, "experimental-webgl"),
+        };
+        return if (matches) cached else null;
     }
 
-    return null;
+    const drawing_context: DrawingContext = blk: {
+        if (std.mem.eql(u8, context_type, "2d")) {
+            const ctx = try page._factory.create(CanvasRenderingContext2D{ ._canvas = self });
+            break :blk .{ .@"2d" = ctx };
+        }
+
+        if (std.mem.eql(u8, context_type, "webgl") or std.mem.eql(u8, context_type, "experimental-webgl")) {
+            const ctx = try page._factory.create(WebGLRenderingContext{});
+            break :blk .{ .webgl = ctx };
+        }
+        return null;
+    };
+    self._cached = drawing_context;
+    return drawing_context;
 }
 
 /// Transfers control of the canvas to an OffscreenCanvas.