Graphics: Fix issue where drawLine for 2px horizontal lines only drew a 1px dot

ChangeLog

@@ -56,6 +56,7 @@
             RegExp: add optimisation for RegExp that is simply checking if a string ends with something
             Bangle.js: .setUI now only clears back widget if it hasn't been hidden by widget_utils
             Fix UtilTimer timings when new task added infront of existing tasks (fix #2575)
+            Graphics: Fix issue where drawLine for 2px horizontal lines only drew a 1px dot
             
      2v24 : Bangle.js2: Add 'Bangle.touchRd()', 'Bangle.touchWr()'
             Bangle.js2: After Bangle.showTestScreen, put Bangle.js into a hard off state (not soft off)

libs/graphics/graphics.c

@@ -645,14 +645,14 @@ void graphicsDrawLine(JsGraphics *gfx, int x1, int y1, int x2, int y2) {
 
   int xl = x2-x1;
   int yl = y2-y1;
-  if (xl<0) xl=-xl; else if (xl==0) xl=1;
-  if (yl<0) yl=-yl; else if (yl==0) yl=1;
+  if (xl<0) xl=-xl;
+  if (yl<0) yl=-yl;
   if (xl > yl) { // longer in X - scan in X
     if (x1>x2) {
       int t;
       t = x1; x1 = x2; x2 = t;
       t = y1; y1 = y2; y2 = t;
-    }
+    } else if (xl==0) xl=1;
     int pos = (y1<<8) + 128; // rounding!
     int step = ((y2-y1)<<8) / xl;
     int x;
@@ -665,7 +665,7 @@ void graphicsDrawLine(JsGraphics *gfx, int x1, int y1, int x2, int y2) {
       int t;
       t = x1; x1 = x2; x2 = t;
       t = y1; y1 = y2; y2 = t;
-    }
+    } else if (yl==0) yl=1;
     int pos = (x1<<8) + 128; // rounding!
     int step = ((x2-x1)<<8) / yl;
     int y;

tests/test_graphics_drawLine.js

@@ -27,11 +27,17 @@ g.setColor(9).setBgColor(0);
 g.drawLine(1,1,14,8);
 g.drawLineAA(1,1+4,14,8+4);
 
+g.setColor(1);
+g.drawLine(10,0,10,0);
+g.drawLine(10,1,11,1);
+g.drawLine(10,2,12,2);
+g.drawLine(10,3,13,3);
+
 SHOULD_BE(`
-                
- @              
-  @@            
-    @@          
+          .     
+ @        ..    
+  @@      ...   
+    @@    ....  
       @@        
  @=     @@      
   +%=     @@