Always diplay sad face on errors; use nullCheck() function; see https://github.com/Microsoft/pxt/issues/302

sim/simlib.ts

@@ -13,6 +13,25 @@ namespace pxsim {
         U.assert(!runtime.board);
         let b = new DalBoard();
         runtime.board = b;
+        runtime.postError = (e) => {
+            led.setBrightness(255);
+            let img = board().ledMatrixState.image;
+            img.clear();
+            img.set(0, 4, 255);
+            img.set(1, 3, 255);
+            img.set(2, 3, 255);
+            img.set(3, 3, 255);
+            img.set(4, 4, 255);
+            img.set(0, 0, 255);
+            img.set(1, 0, 255);
+            img.set(0, 1, 255);
+            img.set(1, 1, 255);
+            img.set(3, 0, 255);
+            img.set(4, 0, 255);
+            img.set(3, 1, 255);
+            img.set(4, 1, 255);
+            runtime.updateDisplay();
+        }
     }
     if (!pxsim.initCurrentRuntime) {
         pxsim.initCurrentRuntime = initRuntimeWithDalBoard;
@@ -195,8 +214,10 @@ namespace pxsim.visuals {
         txtYOffFactor = txtYOffFactor || 0.3;
         const xOff = txtXOffFactor * size * txt.length;
         const yOff = txtYOffFactor * size;
-        svg.hydrate(el, {style: `font-size:${size}px;`,
+        svg.hydrate(el, {
-            transform: `translate(${cx} ${cy}) rotate(${rot}) translate(${xOff} ${yOff})` });
+            style: `font-size:${size}px;`,
+            transform: `translate(${cx} ${cy}) rotate(${rot}) translate(${xOff} ${yOff})`
+        });
         svg.addClass(el, "noselect");
         el.textContent = txt;
         return el;

sim/state/ledmatrix.ts

@@ -195,26 +195,24 @@ namespace pxsim.images {
 
 namespace pxsim.ImageMethods {
     export function showImage(leds: Image, offset: number) {
-        if (!leds) panic(PanicCode.MICROBIT_NULL_DEREFERENCE);
+        pxtrt.nullCheck(leds)
-
         leds.copyTo(offset, 5, board().ledMatrixState.image, 0)
         runtime.queueDisplayUpdate()
     }
 
     export function plotImage(leds: Image, offset: number): void {
-        if (!leds) panic(PanicCode.MICROBIT_NULL_DEREFERENCE);
+        pxtrt.nullCheck(leds)
-
         leds.copyTo(offset, 5, board().ledMatrixState.image, 0)
         runtime.queueDisplayUpdate()
     }
 
     export function height(leds: Image): number {
-        if (!leds) panic(PanicCode.MICROBIT_NULL_DEREFERENCE);
+        pxtrt.nullCheck(leds)
         return Image.height;
     }
 
     export function width(leds: Image): number {
-        if (!leds) panic(PanicCode.MICROBIT_NULL_DEREFERENCE);
+        pxtrt.nullCheck(leds)
         return leds.width;
     }
 
@@ -227,35 +225,32 @@ namespace pxsim.ImageMethods {
     }
 
     export function pixel(leds: Image, x: number, y: number): number {
-        if (!leds) panic(PanicCode.MICROBIT_NULL_DEREFERENCE);
+        pxtrt.nullCheck(leds)
         return leds.get(x, y);
     }
 
     export function setPixel(leds: Image, x: number, y: number, v: number) {
-        if (!leds) panic(PanicCode.MICROBIT_NULL_DEREFERENCE);
+        pxtrt.nullCheck(leds)
         leds.set(x, y, v);
     }
 
     export function clear(leds: Image) {
-        if (!leds) panic(PanicCode.MICROBIT_NULL_DEREFERENCE);
+        pxtrt.nullCheck(leds)
-
         leds.clear();
     }
 
     export function setPixelBrightness(i: Image, x: number, y: number, b: number) {
-        if (!i) panic(PanicCode.MICROBIT_NULL_DEREFERENCE);
+        pxtrt.nullCheck(i)
-
         i.set(x, y, b);
     }
 
     export function pixelBrightness(i: Image, x: number, y: number): number {
-        if (!i) panic(PanicCode.MICROBIT_NULL_DEREFERENCE);
+        pxtrt.nullCheck(i)
-
         return i.get(x, y);
     }
 
     export function scrollImage(leds: Image, stride: number, interval: number): void {
-        if (!leds) panic(PanicCode.MICROBIT_NULL_DEREFERENCE);
+        pxtrt.nullCheck(leds)
         if (stride == 0) stride = 1;
 
         let cb = getResume();

sim/state/misc.ts

@@ -19,24 +19,6 @@ namespace pxsim {
 
     export function panic(code: number) {
         console.log("PANIC:", code)
-        led.setBrightness(255);
-        let img = board().ledMatrixState.image;
-        img.clear();
-        img.set(0, 4, 255);
-        img.set(1, 3, 255);
-        img.set(2, 3, 255);
-        img.set(3, 3, 255);
-        img.set(4, 4, 255);
-        img.set(0, 0, 255);
-        img.set(1, 0, 255);
-        img.set(0, 1, 255);
-        img.set(1, 1, 255);
-        img.set(3, 0, 255);
-        img.set(4, 0, 255);
-        img.set(3, 1, 255);
-        img.set(4, 1, 255);
-        runtime.updateDisplay();
-
         throw new Error("PANIC " + code)
     }