Add grid color and opacity controls

Edge shader now takes u_edge_color and u_edge_opacity uniforms.
Grid section added to sidebar with a color picker and opacity slider.
Blending enabled around edge draw call to support sub-1 opacity.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

standalone/goldberg-sphere/index.html

@@ -133,6 +133,19 @@
 		</div>
 	</div>
 
+	<div>
+		<h3>Grid</h3>
+		<div class="param" style="margin-top:6px">
+			<label>Color</label>
+			<div id="grid-color-btn" style="flex:1; height:22px; border:1px solid #1e3448; cursor:pointer; border-radius:2px;" title="Pick color…"></div>
+		</div>
+		<div class="param">
+			<label>Opacity</label>
+			<input type="range" id="grid-opacity" min="0" max="1" step="0.01" value="1">
+			<span class="val" id="grid-opacity-val">1.00</span>
+		</div>
+	</div>
+
 	<div>
 		<h3>Noise</h3>
 		<div style="display:flex; gap:3px; margin-top:6px; flex-wrap:wrap">

standalone/goldberg-sphere/playground_main.mjs

@@ -31,6 +31,7 @@ const spin       = new Spin_State();
 const paint      = new Paint_State();
 const undo_state = new Undo_State();
 const env        = new Env_State();
+const grid_state = { color: [0.05, 0.05, 0.05], opacity: 1.0 };
 let current_geo      = null;
 let current_palette  = DEFAULT_PALETTE;
 let building         = false;
@@ -681,10 +682,15 @@ function render_frame(ts) {
 	gl.disable(gl.POLYGON_OFFSET_FILL);
 	gl.useProgram(edge_prog);
 	gl.uniformMatrix4fv(gl.getUniformLocation(edge_prog, 'u_mvp'), false, mvp);
+	gl.uniform3fv(gl.getUniformLocation(edge_prog, 'u_edge_color'),   grid_state.color);
+	gl.uniform1f(gl.getUniformLocation(edge_prog,  'u_edge_opacity'), grid_state.opacity);
+	gl.enable(gl.BLEND);
+	gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);
 	const ep = gl.getAttribLocation(edge_prog, 'a_pos');
 	gl.bindBuffer(gl.ARRAY_BUFFER, edge_pos_buf); gl.enableVertexAttribArray(ep); gl.vertexAttribPointer(ep, 3, gl.FLOAT, false, 0, 0);
 	gl.drawArrays(gl.LINES, 0, edge_verts);
 	gl.disableVertexAttribArray(ep);
+	gl.disable(gl.BLEND);
 
 
 	gl.enable(gl.POLYGON_OFFSET_FILL);
@@ -1073,6 +1079,42 @@ function _hsl_to_rgb(h,s,l) {
 	sync_env_ui();
 }
 
+// ---------------------------------------------------------------------------
+// Grid UI wiring
+// ---------------------------------------------------------------------------
+
+{
+	const btn     = document.getElementById('grid-color-btn');
+	const opacity = document.getElementById('grid-opacity');
+	const opacity_val = document.getElementById('grid-opacity-val');
+
+	const hex_from = c => {
+		const h = v => Math.round(Math.min(v, 1) * 255).toString(16).padStart(2, '0');
+		return `#${h(c[0])}${h(c[1])}${h(c[2])}`;
+	};
+
+	btn.style.background = hex_from(grid_state.color);
+	btn.addEventListener('click', () => {
+		color_dialog_open({
+			get: () => hex_from(grid_state.color),
+			set: hex => {
+				const r = parseInt(hex.slice(1, 3), 16) / 255;
+				const g = parseInt(hex.slice(3, 5), 16) / 255;
+				const b = parseInt(hex.slice(5, 7), 16) / 255;
+				grid_state.color = [r, g, b];
+				btn.style.background = hex;
+				request_render();
+			},
+		});
+	});
+
+	opacity.addEventListener('input', () => {
+		grid_state.opacity = parseFloat(opacity.value);
+		opacity_val.textContent = grid_state.opacity.toFixed(2);
+		request_render();
+	});
+}
+
 // ---------------------------------------------------------------------------
 // Keyboard shortcuts
 // ---------------------------------------------------------------------------

standalone/goldberg-sphere/shaders/edge.frag

@@ -1,2 +1,4 @@
 precision mediump float;
-void main() { gl_FragColor = vec4(0.05, 0.05, 0.05, 1.0); }
+uniform vec3 u_edge_color;
+uniform float u_edge_opacity;
+void main() { gl_FragColor = vec4(u_edge_color, u_edge_opacity); }