Add 2D canvas mode compacted to the steps, ocean-chaos and reef-2d shaders

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/test_treppe_gl.py

@@ -68,3 +68,40 @@ def test_brightness_scales_and_clamps():
     assert t.to_rgbw(px, "extract", 0).max() == 0
     np.testing.assert_allclose(t.to_rgbw(px, "extract", 500),
                                t.to_rgbw(px, "extract", 100))
+
+
+CANVAS_SHADER = """
+void mainImage(out vec4 c, in vec2 p) {
+    // red in the two lowest rows, and in the two leftmost columns (step 0)
+    c = vec4(p.y < 2.0 ? 1.0 : 0.0, p.x < 2.0 ? 1.0 : 0.0, 0.0, 1.0);
+}"""
+
+
+def test_canvas_compaction_modes():
+    ctx, _ = t.create_context(window=False)
+    r = t.Renderer(ctx)
+    r.load(CANVAS_SHADER)
+    r.configure((32, 4), "mean")      # 2 columns per step, 4 rows
+    px = r.render_strip(0.0)
+    assert px.shape == (16, 4)
+    np.testing.assert_allclose(px[:, 0], 0.5)                 # 2 of 4 rows
+    np.testing.assert_allclose(px[0, 1], 1.0)                 # step 0 green
+    np.testing.assert_allclose(px[1:, 1], 0.0)
+    r.configure((32, 4), "max")
+    np.testing.assert_allclose(r.render_strip(0.0)[:, 0], 1.0)
+    r.configure((32, 4), "row")                               # row 2 is dark
+    np.testing.assert_allclose(r.render_strip(0.0)[:, 0], 0.0)
+    r.configure(None)                                         # back to 1D
+    assert r.render_strip(0.0).shape == (16, 4)
+
+
+def test_canvas_parsing():
+    assert t.parse_canvas("256x32") == (256, 32)
+    for bad in ("100x10", "abc", "8x8", "256x0"):
+        with pytest.raises(ValueError):
+            t.parse_canvas(bad)
+    assert t.directive("// x\n// canvas: 128x16 compact: max\nvoid f(){}") == (
+        (128, 16), "max")
+    assert t.directive("void mainImage() {}") == (None, None)
+    with pytest.raises(ValueError):
+        t.directive("// canvas: 128x16 compact: nope")