diff --git a/deps/Makefile b/deps/Makefile
index c82a263..96b61c9 100644
--- a/deps/Makefile
+++ b/deps/Makefile
@@ -144,6 +144,15 @@ CMAKE += -DCMAKE_CXX_COMPILER_AR=$(CMAKE_AR)
 CMAKE += -DCMAKE_RANLIB=$(CMAKE_RANLIB)
 CMAKE += -DCMAKE_C_COMPILER_RANLIB=$(CMAKE_RANLIB)
 CMAKE += -DCMAKE_CXX_COMPILER_RANLIB=$(CMAKE_RANLIB)
+ifeq ($(shell uname -s),Darwin)
+CMAKE += -DCMAKE_CROSSCOMPILING=ON
+CMAKE += -DCMAKE_SYSTEM_NAME=Generic
+endif
+endif
+
+# fix cmake forcing SDK for us
+ifeq ($(MACOS),true)
+CMAKE += -DCMAKE_OSX_SYSROOT="macosx"
 endif
 
 # fix cross-compilation for windows
diff --git a/src/emscripten/shell.html b/src/emscripten/shell.html
index d886116..8a372f8 100644
--- a/src/emscripten/shell.html
+++ b/src/emscripten/shell.html
@@ -27,7 +27,7 @@
         display: none;
         image-rendering: pixelated;
         image-rendering: crisp-edges;
-        position: absolute;
+        position: fixed;
         transform-origin: 0 0 0;
         transform: scale(calc(1 / var(--device-pixel-ratio)));
         width: 100vw;
@@ -93,6 +93,7 @@
       <div class="spinner"></div>
       <center style="margin-top:0.5em"><strong>Cardinal</strong></center>
     </figure>
+    <div class="emscripten" id="error"></div>
     <div class="emscripten" id="status">Downloading...</div>
     <div class="emscripten">
       <progress value="0" max="100" id="progress" hidden=1></progress>
@@ -103,68 +104,97 @@
     </div>
 
     <script type='text/javascript'>
+      'use strict';
+
+      var wasmErrors = [];
       var errorElement = document.getElementById('error');
       var statusElement = document.getElementById('status');
       var progressElement = document.getElementById('progress');
       var spinnerElement = document.getElementById('spinner');
-      var canvasWrapper = document.getElementById('canvas_wrapper');
 
-      var Module = {
-        preRun: [],
-        postRun: function() {
-          statusElement.style.display = 'none';
-          progressElement.style.display = 'none';
-          spinnerElement.style.display = 'none';
-          canvasWrapper.style.display = 'block';
-          window.dispatchEvent(new Event('resize'));
-        },
-        canvas: (function() {
-          var canvas = document.getElementById('canvas');
-
-          // As a default initial behavior, pop up an alert when webgl context is lost. To make your
-          // application robust, you may want to override this behavior before shipping!
-          // See http://www.khronos.org/registry/webgl/specs/latest/1.0/#5.15.2
-          canvas.addEventListener("webglcontextlost", function(e) { alert('WebGL context lost. You will need to reload the page.'); e.preventDefault(); }, false);
-
-          return canvas;
-        })(),
-        setStatus: function(text) {
-          if (!Module.setStatus.last) Module.setStatus.last = { time: Date.now(), text: '' };
-          if (text === Module.setStatus.last.text) return;
-          var m = text.match(/([^(]+)\((\d+(\.\d+)?)\/(\d+)\)/);
-          var now = Date.now();
-          if (m && now - Module.setStatus.last.time < 30) return; // if this is a progress update, skip it if too soon
-          Module.setStatus.last.time = now;
-          Module.setStatus.last.text = text;
-          if (m) {
-            text = m[1];
-            progressElement.value = parseInt(m[2])*100;
-            progressElement.max = parseInt(m[4])*100;
-            progressElement.hidden = false;
-            spinnerElement.hidden = false;
-          } else {
-            progressElement.value = null;
-            progressElement.max = null;
-            progressElement.hidden = true;
-            if (!text) spinnerElement.hidden = true;
-          }
-          statusElement.innerHTML = text;
-        },
-        totalDependencies: 0,
-        monitorRunDependencies: function(left) {
-          this.totalDependencies = Math.max(this.totalDependencies, left);
-          Module.setStatus(left ? 'Preparing... (' + (this.totalDependencies-left) + '/' + this.totalDependencies + ')' : 'All downloads complete.');
+      if (typeof(WebAssembly) === "undefined") {
+        wasmErrors.push('WebAssembly unsupported');
+      } else {
+        if (!WebAssembly.validate(new Uint8Array([0,97,115,109,1,0,0,0,1,4,1,96,0,0,3,2,1,0,5,3,1,0,1,10,14,1,12,0,65,0,65,0,65,0,252,10,0,0,11]))) {
+          wasmErrors.push('Bulk Memory Operations unsupported');
         }
-      };
-      Module.setStatus('Downloading...');
-      window.onerror = function() {
-        errorElement.innerHTML = 'Exception thrown:<br>' + err
+        if (!WebAssembly.validate(new Uint8Array([0,97,115,109,1,0,0,0,1,4,1,96,0,0,3,2,1,0,10,8,1,6,0,6,64,25,11,11]))) {
+          wasmErrors.push('Exception handling unsupported');
+        }
+        if (!WebAssembly.validate(new Uint8Array([0,97,115,109,1,0,0,0,2,8,1,1,97,1,98,3,127,1,6,6,1,127,1,65,0,11,7,5,1,1,97,3,1]))) {
+          wasmErrors.push('Importable/Exportable mutable globals unsupported');
+        }
+        if (!WebAssembly.validate(new Uint8Array([0,97,115,109,1,0,0,0,1,5,1,96,0,1,123,3,2,1,0,10,10,1,8,0,65,0,253,15,253,98,11]))) {
+          wasmErrors.push('Fixed-Width SIMD unsupported');
+        }
+      }
+
+      if (wasmErrors.length !== 0) {
+        errorElement.innerHTML = 'Cannot start Cardinal:<br>' + wasmErrors.join('<br>') + '<br><br>Perhaps try a different browser?';
         errorElement.style.display = 'block';
+        statusElement.style.display = 'none';
+        progressElement.style.display = 'none';
         spinnerElement.style.display = 'none';
-        Module.setStatus = function(text) {
-          if (text) console.error('[post-exception status] ' + text);
+      } else {
+        var canvasWrapper = document.getElementById('canvas_wrapper');
+
+        var Module = {
+          preRun: [],
+          postRun: function() {
+            statusElement.style.display = 'none';
+            progressElement.style.display = 'none';
+            spinnerElement.style.display = 'none';
+            canvasWrapper.style.display = 'block';
+            window.dispatchEvent(new Event('resize'));
+          },
+          canvas: (function() {
+            var canvas = document.getElementById('canvas');
+
+            // As a default initial behavior, pop up an alert when webgl context is lost. To make your
+            // application robust, you may want to override this behavior before shipping!
+            // See http://www.khronos.org/registry/webgl/specs/latest/1.0/#5.15.2
+            canvas.addEventListener("webglcontextlost", function(e) { alert('WebGL context lost. You will need to reload the page.'); e.preventDefault(); }, false);
+
+            return canvas;
+          })(),
+          setStatus: function(text) {
+            if (!Module.setStatus.last) Module.setStatus.last = { time: Date.now(), text: '' };
+            if (text === Module.setStatus.last.text) return;
+            var m = text.match(/([^(]+)\((\d+(\.\d+)?)\/(\d+)\)/);
+            var now = Date.now();
+            if (m && now - Module.setStatus.last.time < 30) return; // if this is a progress update, skip it if too soon
+            Module.setStatus.last.time = now;
+            Module.setStatus.last.text = text;
+            if (m) {
+              text = m[1];
+              progressElement.value = parseInt(m[2])*100;
+              progressElement.max = parseInt(m[4])*100;
+              progressElement.hidden = false;
+              spinnerElement.hidden = false;
+            } else {
+              progressElement.value = null;
+              progressElement.max = null;
+              progressElement.hidden = true;
+              if (!text) spinnerElement.hidden = true;
+            }
+            statusElement.innerHTML = text;
+          },
+          totalDependencies: 0,
+          monitorRunDependencies: function(left) {
+            this.totalDependencies = Math.max(this.totalDependencies, left);
+            Module.setStatus(left ? 'Preparing... (' + (this.totalDependencies-left) + '/' + this.totalDependencies + ')' : 'All downloads complete.');
+          }
         };
-      };
+        Module.setStatus('Downloading...');
+        window.onerror = function(err) {
+          errorElement.innerHTML = 'Exception thrown:<br>' + err
+          errorElement.style.display = 'block';
+          spinnerElement.style.display = 'none';
+          Module.setStatus = function(text) {
+            if (text) console.error('[post-exception status] ' + text);
+          };
+        };
+      }
     </script>
     {{{ SCRIPT }}}
   </body>