no-wrap option; pivoted exponential zoom

client/world/pivot_zoom_test.go

@@ -0,0 +1,50 @@
+package world
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestPivotZoom_CursorAtCenter_KeepsCamera(t *testing.T) {
+	t.Parallel()
+
+	cx, cy := PivotZoomCameraNoWrap(
+		50*SCALE, 60*SCALE,
+		100, 80,
+		50, 40, // cursor at center
+		SCALE, 2*SCALE,
+	)
+	require.Equal(t, 50*SCALE, cx)
+	require.Equal(t, 60*SCALE, cy)
+}
+
+func TestPivotZoom_RightEdge_ZoomInMovesCameraRight(t *testing.T) {
+	t.Parallel()
+
+	// viewport 100px, cursor at x=100 (right edge), center is 50 => offX=50px
+	// zoom 1->2 halves worldPerPx, so camera must move towards the cursor to keep the same world point.
+	cx0 := 50 * SCALE
+
+	cx, _ := PivotZoomCameraNoWrap(
+		cx0, 50*SCALE,
+		100, 100,
+		100, 50,
+		SCALE, 2*SCALE,
+	)
+	require.Greater(t, cx, cx0)
+}
+
+func TestPivotZoom_LeftEdge_ZoomInMovesCameraLeft(t *testing.T) {
+	t.Parallel()
+
+	cx0 := 50 * SCALE
+
+	cx, _ := PivotZoomCameraNoWrap(
+		cx0, 50*SCALE,
+		100, 100,
+		0, 50,
+		SCALE, 2*SCALE,
+	)
+	require.Less(t, cx, cx0)
+}