ebiten: Add a shader test

Updates #1283

shader_test.go

@@ -0,0 +1,47 @@
+// Copyright 2020 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ebiten_test
+
+import (
+	"image/color"
+	"testing"
+
+	. "github.com/hajimehoshi/ebiten"
+)
+
+func TestShaderFill(t *testing.T) {
+	const w, h = 16, 16
+
+	dst, _ := NewImage(8, 8, FilterDefault)
+	s, err := NewShader([]byte(`package main
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	return vec4(1, 0, 0, 1)
+}
+`))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	dst.DrawRectShader(16, 16, s, nil)
+
+	if got, want := dst.At(0, 0).(color.RGBA), (color.RGBA{0xff, 0, 0, 0xff}); got != want {
+		t.Errorf("got: %v, want: %v", got, want)
+	}
+
+	if got, want := dst.At(w-1, h-1).(color.RGBA), (color.RGBA{}); got != want {
+		t.Errorf("got: %v, want: %v", got, want)
+	}
+}