WebGLRenderer: rebind shared vertex buffer on batcher switch

setBatcher() now rebinds the renderer's shared vertex buffer before
activating a new batcher. This allows custom batchers that use their
own GL buffers (e.g. SpineBatcher) to integrate without manual cleanup.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: obiot

packages/melonjs/src/video/webgl/webgl_renderer.js

@@ -358,6 +358,8 @@ export default class WebGLRenderer extends Renderer {
 				// flush the current batcher
 				this.currentBatcher.flush();
 			}
+			// rebind the renderer's shared vertex buffer (custom batchers may have bound their own)
+			this.gl.bindBuffer(this.gl.ARRAY_BUFFER, this.vertexBuffer);
 			this.currentBatcher = batcher;
 			this.currentBatcher.bind();
 		}
@@ -744,15 +746,19 @@ export default class WebGLRenderer extends Renderer {
 	 * and will always fall back to "normal" in WebGL. <br>
 	 * @see https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/globalCompositeOperation
 	 * @param {string} [mode="normal"] - blend mode
-	 * @param {WebGLRenderingContext} [gl] - a WebGL context
+	 * @param {boolean} [premultipliedAlpha=true] - whether textures use premultiplied alpha (affects source blend factor)
 	 * @returns {string} the blend mode actually applied (may differ if the requested mode is unsupported)
 	 */
-	setBlendMode(mode = "normal", gl = this.gl) {
+	setBlendMode(mode = "normal", premultipliedAlpha = true) {
 		if (this.currentBlendMode !== mode) {
+			const gl = this.gl;
 			this.flush();
 			gl.enable(gl.BLEND);
 			this.currentBlendMode = mode;
 
+			// source factor depends on whether textures use premultiplied alpha
+			const srcAlpha = premultipliedAlpha ? gl.ONE : gl.SRC_ALPHA;
+
 			switch (mode) {
 				case "screen":
 					gl.blendEquation(gl.FUNC_ADD);
@@ -763,7 +769,7 @@ export default class WebGLRenderer extends Renderer {
 				case "additive":
 				case "add":
 					gl.blendEquation(gl.FUNC_ADD);
-					gl.blendFunc(gl.ONE, gl.ONE);
+					gl.blendFunc(srcAlpha, gl.ONE);
 					break;
 
 				case "multiply":
@@ -777,7 +783,7 @@ export default class WebGLRenderer extends Renderer {
 						gl.blendFunc(gl.ONE, gl.ONE);
 					} else {
 						gl.blendEquation(gl.FUNC_ADD);
-						gl.blendFunc(gl.ONE, gl.ONE_MINUS_SRC_ALPHA);
+						gl.blendFunc(srcAlpha, gl.ONE_MINUS_SRC_ALPHA);
 						this.currentBlendMode = "normal";
 					}
 					break;
@@ -788,14 +794,14 @@ export default class WebGLRenderer extends Renderer {
 						gl.blendFunc(gl.ONE, gl.ONE);
 					} else {
 						gl.blendEquation(gl.FUNC_ADD);
-						gl.blendFunc(gl.ONE, gl.ONE_MINUS_SRC_ALPHA);
+						gl.blendFunc(srcAlpha, gl.ONE_MINUS_SRC_ALPHA);
 						this.currentBlendMode = "normal";
 					}
 					break;
 
 				default:
 					gl.blendEquation(gl.FUNC_ADD);
-					gl.blendFunc(gl.ONE, gl.ONE_MINUS_SRC_ALPHA);
+					gl.blendFunc(srcAlpha, gl.ONE_MINUS_SRC_ALPHA);
 					this.currentBlendMode = "normal";
 					break;
 			}