Merge pull request #232 from arduino/fix-226

Fix: prevent artefacts from appearing on the screen during a SCROLL_LEFT.

Author: aentinger

libraries/Arduino_LED_Matrix/examples/TextWithArduinoGraphics/TextWithArduinoGraphics.ino

@@ -5,22 +5,20 @@
 ArduinoLEDMatrix matrix;
 
 void setup() {
-  Serial.begin(115200);
   matrix.begin();
 
   matrix.beginDraw();
+
   matrix.stroke(0xFFFFFFFF);
-  // add some static text
-  // will only show "UNO" (not enough space on the display)
-  const char text[] = "UNO r4";
+  matrix.textScrollSpeed(100);
+
+  const char text[] = "  UNO r4  ";
   matrix.textFont(Font_4x6);
   matrix.beginText(0, 1, 0xFFFFFF);
   matrix.println(text);
-  matrix.endText();
+  matrix.endText(SCROLL_LEFT);
 
   matrix.endDraw();
-
-  delay(2000);
 }
 
 void loop() {

libraries/Arduino_LED_Matrix/src/Arduino_LED_Matrix.h

@@ -250,7 +250,7 @@ class ArduinoLEDMatrix
 
 #ifdef MATRIX_WITH_ARDUINOGRAPHICS
     virtual void set(int x, int y, uint8_t r, uint8_t g, uint8_t b) {
-      if (y >= canvasHeight || x >= canvasWidth) {
+      if (y >= canvasHeight || x >= canvasWidth || y < 0 || x < 0) {
         return;
       }
       // the r parameter is (mis)used to set the character to draw with