diff --git a/wasm/shims/gl_immediate_shim.js b/wasm/shims/gl_immediate_shim.js
new file mode 100644
index 0000000..0d71567
--- /dev/null
+++ b/wasm/shims/gl_immediate_shim.js
@@ -0,0 +1,178 @@
+/**
+ * gl_immediate_shim.js
+ *
+ * Custom OpenGL immediate mode shims for KiCad WASM port.
+ * Fixes Emscripten LEGACY_GL_EMULATION issues:
+ * 1. Color-per-vertex requirement - injects color before each vertex automatically
+ * 2. Missing double-precision functions (glVertex2d, glVertex3d, glColor3d, glColor4d)
+ *
+ * Usage: emcc ... --js-library=lib/gl_immediate_shim.js
+ */
+
+addToLibrary({
+  // ==================================================================
+  // GLImmediateShim - State tracking and function wrapping
+  // ==================================================================
+
+  $GLImmediateShim__deps: ['$GLImmediate', 'glBegin', 'glEnd', 'glVertex2f', 'glVertex3f', 'glColor3f', 'glColor4f'],
+  $GLImmediateShim__postset: 'GLImmediateShim.init();',
+  $GLImmediateShim: {
+    // Current color state (persistent across vertices)
+    currentColor: null,
+
+    // Track if we're inside glBegin/glEnd block
+    inBeginEnd: false,
+
+    // Track if color was called since the last vertex
+    // This prevents double-injection when code already calls color per vertex
+    colorCalledSinceLastVertex: false,
+
+    // Original functions we're wrapping
+    origFns: {},
+
+    // Initialization flag
+    initialized: false,
+
+    init: function() {
+      if (GLImmediateShim.initialized) return;
+      if (typeof GLImmediate === 'undefined') {
+        // GLImmediate not ready yet, will be called again
+        console.log('[GLImmediateShim] Waiting for GLImmediate...');
+        return;
+      }
+
+      console.log('[GLImmediateShim] Initializing OpenGL immediate mode shims');
+
+      // Initialize current color to white (OpenGL default)
+      GLImmediateShim.currentColor = new Float32Array([1.0, 1.0, 1.0, 1.0]);
+
+      // Store original functions
+      GLImmediateShim.origFns = {
+        glBegin: _glBegin,
+        glEnd: _glEnd,
+        glVertex2f: _glVertex2f,
+        glVertex3f: _glVertex3f,
+        glColor3f: _glColor3f,
+        glColor4f: _glColor4f,
+      };
+
+      // Install shims
+      _glBegin = GLImmediateShim.shimBegin;
+      _glEnd = GLImmediateShim.shimEnd;
+      _glVertex2f = GLImmediateShim.shimVertex2f;
+      _glVertex3f = GLImmediateShim.shimVertex3f;
+      _glColor3f = GLImmediateShim.shimColor3f;
+      _glColor4f = GLImmediateShim.shimColor4f;
+
+      GLImmediateShim.initialized = true;
+      console.log('[GLImmediateShim] Initialized successfully');
+    },
+
+    // ==================================================================
+    // Shim implementations
+    // ==================================================================
+
+    shimBegin: function(mode) {
+      GLImmediateShim.inBeginEnd = true;
+      GLImmediateShim.colorCalledSinceLastVertex = false;
+      GLImmediateShim.origFns.glBegin(mode);
+    },
+
+    shimEnd: function() {
+      GLImmediateShim.inBeginEnd = false;
+      GLImmediateShim.origFns.glEnd();
+    },
+
+    shimColor3f: function(r, g, b) {
+      var c = GLImmediateShim.currentColor;
+      c[0] = r;
+      c[1] = g;
+      c[2] = b;
+      c[3] = 1.0;
+
+      if (GLImmediateShim.inBeginEnd) {
+        // Mark that color was explicitly called for this vertex
+        GLImmediateShim.colorCalledSinceLastVertex = true;
+      }
+
+      GLImmediateShim.origFns.glColor3f(r, g, b);
+    },
+
+    shimColor4f: function(r, g, b, a) {
+      var c = GLImmediateShim.currentColor;
+      c[0] = r;
+      c[1] = g;
+      c[2] = b;
+      c[3] = a;
+
+      if (GLImmediateShim.inBeginEnd) {
+        // Mark that color was explicitly called for this vertex
+        GLImmediateShim.colorCalledSinceLastVertex = true;
+      }
+
+      GLImmediateShim.origFns.glColor4f(r, g, b, a);
+    },
+
+    // Inject current color before each vertex (only if not already called)
+    injectColor: function() {
+      if (!GLImmediateShim.inBeginEnd) return;
+
+      // Only inject color if it wasn't already called for this vertex
+      if (!GLImmediateShim.colorCalledSinceLastVertex) {
+        var c = GLImmediateShim.currentColor;
+        GLImmediateShim.origFns.glColor4f(c[0], c[1], c[2], c[3]);
+      }
+
+      // Reset the flag for the next vertex
+      GLImmediateShim.colorCalledSinceLastVertex = false;
+    },
+
+    shimVertex2f: function(x, y) {
+      GLImmediateShim.injectColor();
+      GLImmediateShim.origFns.glVertex2f(x, y);
+    },
+
+    shimVertex3f: function(x, y, z) {
+      GLImmediateShim.injectColor();
+      GLImmediateShim.origFns.glVertex3f(x, y, z);
+    },
+  },
+
+  // ==================================================================
+  // Double-precision vertex functions (missing in Emscripten)
+  // ==================================================================
+
+  glVertex2d__deps: ['glVertex2f'],
+  glVertex2d: function(x, y) {
+    _glVertex2f(x, y);
+  },
+
+  glVertex3d__deps: ['glVertex3f'],
+  glVertex3d: function(x, y, z) {
+    _glVertex3f(x, y, z);
+  },
+
+  glVertex4d__deps: ['glVertex4f'],
+  glVertex4d: function(x, y, z, w) {
+    _glVertex4f(x, y, z, w);
+  },
+
+  // ==================================================================
+  // Double-precision color functions
+  // ==================================================================
+
+  glColor3d__deps: ['glColor3f'],
+  glColor3d: function(r, g, b) {
+    _glColor3f(r, g, b);
+  },
+
+  glColor4d__deps: ['glColor4f'],
+  glColor4d: function(r, g, b, a) {
+    _glColor4f(r, g, b, a);
+  },
+});
+
+// Ensure GLImmediateShim is included in the build
+if (typeof extraLibraryFuncs !== 'undefined') {
+  extraLibraryFuncs.push('$GLImmediateShim');
+}