render: expose WebGL as unavailable without backend

crates/obscura-js/js/bootstrap.js

@@ -7279,51 +7279,12 @@ Element.prototype.getContext = function getContext(type) {
     return this._ctx;
   }
   if (type === 'webgl' || type === 'experimental-webgl' || type === 'webgl2') {
-    return {
-      canvas: this,
-      MAX_VIEWPORT_DIMS: 0x0D33,
-      MAX_TEXTURE_SIZE: 0x0D33,
-      MAX_RENDERBUFFER_SIZE: 0x84E8,
-      MAX_TEXTURE_MAX_ANISOTROPY_EXT: 0x84EA,
-      MAX_DRAW_BUFFERS_WEBGL: 0x8824,
-      getContextAttributes() { return { alpha: true, antialias: true, depth: true, failIfMajorPerformanceCaveat: false, powerPreference: "default", premultipliedAlpha: true, preserveDrawingBuffer: false, stencil: true, desynchronized: false }; },
-      uniform2f() {},
-      getExtension(name) {
-        if (name === 'WEBGL_debug_renderer_info') return { UNMASKED_VENDOR_WEBGL: 0x9245, UNMASKED_RENDERER_WEBGL: 0x9246 };
-        return null;
-      },
-      getParameter(pname) {
-        if (pname === 0x9245) return _fp('gpuVendor');
-        if (pname === 0x9246) return _fp('gpu');
-        if (pname === 0x1F01) return 'WebKit WebGL';  // GL_RENDERER
-        if (pname === 0x1F00) return 'WebKit';          // GL_VENDOR
-        if (pname === 0x1F02) return 'OpenGL ES 3.0 (ANGLE)'; // GL_VERSION
-        if (pname === 0x8B8C) return 'WebGL GLSL ES 3.00 (ANGLE)'; // GL_SHADING_LANGUAGE_VERSION
-        if (pname === undefined) return [0, 0];
-        // Some properties like MAX_VIEWPORT_DIMS return arrays
-        if (pname === 0x0D33) return [8192, 8192];
-        if (pname === 0x8A2A) return [8192, 8192];
-        return 0;
-      },
-      getSupportedExtensions() { return ['WEBGL_debug_renderer_info','EXT_texture_filter_anisotropic','WEBGL_compressed_texture_s3tc','WEBGL_lose_context']; },
-      getShaderPrecisionFormat() { return { rangeMin: 127, rangeMax: 127, precision: 23 }; },
-      createBuffer() { return {}; }, createShader() { return {}; }, createProgram() { return {}; },
-      shaderSource() {}, compileShader() {}, attachShader() {}, linkProgram() {},
-      getProgramParameter() { return true; }, useProgram() {}, deleteShader() {},
-      bindBuffer() {}, bufferData() {}, enableVertexAttribArray() {}, vertexAttribPointer() {},
-      drawArrays() {}, drawElements() {}, viewport() {}, clear() {}, clearColor() {},
-      enable() {}, disable() {}, blendFunc() {}, depthFunc() {},
-      getUniformLocation() { return {}; }, getAttribLocation() { return 0; },
-      uniform1f() {}, uniform1i() {}, uniformMatrix4fv() {},
-      createTexture() { return {}; }, bindTexture() {}, texImage2D() {}, texParameteri() {},
-      activeTexture() {}, pixelStorei() {}, generateMipmap() {},
-      createFramebuffer() { return {}; }, bindFramebuffer() {}, framebufferTexture2D() {},
-      readPixels(x,y,w,h,f,t,d) { if(d) for(let i=0;i<d.length;i++) d[i]=Math.floor(Math.random()*256); },
-      VERTEX_SHADER: 0x8B31, FRAGMENT_SHADER: 0x8B30, LINK_STATUS: 0x8B82,
-      ARRAY_BUFFER: 0x8892, STATIC_DRAW: 0x88E4, FLOAT: 0x1406,
-      TRIANGLES: 0x0004, COLOR_BUFFER_BIT: 0x4000, DEPTH_BUFFER_BIT: 0x100,
-      TEXTURE_2D: 0x0DE1, RGBA: 0x1908, UNSIGNED_BYTE: 0x1401,
-    };
+    // Context creation is allowed to fail, and that is the only truthful
+    // behavior until the renderer has a real WebGL backend. The former shim
+    // reported successful shader/program creation while every draw call was a
+    // no-op. Feature-detecting applications consequently selected their WebGL
+    // path, hid their HTML/image fallback, and produced a blank canvas.
+    return null;
   }
   return null;
 };

crates/obscura-js/src/runtime.rs

@@ -2794,6 +2794,36 @@ mod tests {
         assert_eq!(result, serde_json::json!([1, 1, true, ""]));
     }
 
+    #[test]
+    fn unavailable_webgl_context_does_not_claim_success() {
+        let mut rt = setup_runtime("<html><body><canvas></canvas></body></html>");
+        let result = rt
+            .evaluate(
+                r#"
+                (() => {
+                    const canvas = document.querySelector('canvas');
+                    const fallback = document.createElement('p');
+                    if (!canvas.getContext('webgl')) {
+                        fallback.textContent = 'static fallback';
+                        document.body.appendChild(fallback);
+                    }
+                    return [
+                        canvas.getContext('webgl'),
+                        canvas.getContext('webgl2'),
+                        canvas.getContext('experimental-webgl'),
+                        fallback.isConnected,
+                        fallback.textContent,
+                    ];
+                })()
+                "#,
+            )
+            .unwrap();
+        assert_eq!(
+            result,
+            serde_json::json!([null, null, null, true, "static fallback"])
+        );
+    }
+
     #[test]
     fn test_script_execution() {
         let mut rt = setup_runtime("<ul><li>A</li><li>B</li></ul>");