Function TestRadialGradientAt

colors_test.go:129–282

(t *testing.T)

}

func TestRadialGradientAt(t *testing.T) {
	red := color.RGBA{255, 0, 0, 255}
	blue := color.RGBA{0, 0, 255, 255}

	// Helper to build a radial gradient with red at t=0 and blue at t=1.
	makeGrad := func(c0 Point, r0 float64, c1 Point, r1 float64) *RadialGradient {
		g := NewRadialGradient(c0, r0, c1, r1)
		g.Add(0.0, red)
		g.Add(1.0, blue)
		return g
	}

	// colorApproxEqual allows small rounding differences from interpolation.
	colorApproxEqual := func(a, b color.RGBA) bool {
		diff := func(x, y uint8) int {
			d := int(x) - int(y)
			if d < 0 {
				return -d
			}
			return d
		}
		return diff(a.R, b.R) <= 1 && diff(a.G, b.G) <= 1 && diff(a.B, b.B) <= 1 && diff(a.A, b.A) <= 1
	}

	tests := []struct {
		name string
		grad *RadialGradient
		x, y float64
		want color.RGBA
	}{
		{
			name: "empty gradient returns transparent",
			grad: NewRadialGradient(Point{0, 0}, 0, Point{0, 0}, 10),
			x:    5,
			y:    0,
			want: Transparent,
		},
		{
			name: "concentric at center returns first stop",
			grad: makeGrad(Point{0, 0}, 0, Point{0, 0}, 10),
			x:    0,
			y:    0,
			want: red,
		},
		{
			name: "concentric at outer edge returns last stop",
			grad: makeGrad(Point{0, 0}, 0, Point{0, 0}, 10),
			x:    10,
			y:    0,
			want: blue,
		},
		{
			name: "concentric beyond outer edge clamps to last stop",
			grad: makeGrad(Point{0, 0}, 0, Point{0, 0}, 10),
			x:    20,
			y:    0,
			want: blue,
		},