[CANVAS] Fix leftover pixels when drawing the home direction arrow

Since the arrow is taller than the width of a grid slow, it overflows
the slot a bit when it's rotated by 90º. Also, simplify the algorithm
for drawing it a bit so it transmits a bit less data per redrawing.

src/main/io/osd.c

@@ -1310,7 +1310,7 @@ static bool osdDrawSingleElement(uint8_t item)
                 else
                 {
                     int homeDirection = GPS_directionToHome - DECIDEGREES_TO_DEGREES(osdGetHeading());
-                    osdDrawDirArrow(osdDisplayPort, osdGetDisplayPortCanvas(), OSD_DRAW_POINT_GRID(elemPosX, elemPosY), homeDirection, true);
+                    osdDrawDirArrow(osdDisplayPort, osdGetDisplayPortCanvas(), OSD_DRAW_POINT_GRID(elemPosX, elemPosY), homeDirection);
                 }
             } else {
                 // No home or no fix or unknown heading, blink.

src/main/io/osd_canvas.c

@@ -120,32 +120,41 @@ void osdCanvasDrawVario(displayPort_t *display, displayCanvas_t *canvas, const o
     prev = zvel;
 }
 
-void osdCanvasDrawDirArrow(displayPort_t *display, displayCanvas_t *canvas, const osdDrawPoint_t *p, float degrees, bool eraseBefore)
+void osdCanvasDrawDirArrow(displayPort_t *display, displayCanvas_t *canvas, const osdDrawPoint_t *p, float degrees)
 {
     UNUSED(display);
 
+    const int top = 6;
+    const int topInset = -2;
+    const int bottom = -6;
+    const int width = 5;
+    // Since grid slots are not square, when we rotate the arrow
+    // it overflows horizontally a bit. Making a square-ish arrow
+    // doesn't look good, so it's better to overstep the grid slot
+    // boundaries a bit and then clean after ourselves.
+    const int overflow = 3;
+
     int px;
     int py;
     osdDrawPointGetPixels(&px, &py, display, canvas, p);
 
-    displayCanvasClipToRect(canvas, px, py, canvas->gridElementWidth, canvas->gridElementHeight);
-
-    if (eraseBefore) {
-        displayCanvasSetFillColor(canvas, DISPLAY_CANVAS_COLOR_TRANSPARENT);
-        displayCanvasFillRect(canvas, px, py, canvas->gridElementWidth, canvas->gridElementHeight);
-    }
+    displayCanvasClearRect(canvas, px - overflow, py, canvas->gridElementWidth + overflow * 2, canvas->gridElementHeight);
 
     displayCanvasSetFillColor(canvas, DISPLAY_CANVAS_COLOR_WHITE);
     displayCanvasSetStrokeColor(canvas, DISPLAY_CANVAS_COLOR_BLACK);
 
     displayCanvasCtmRotate(canvas, -DEGREES_TO_RADIANS(180 + degrees));
     displayCanvasCtmTranslate(canvas, px + canvas->gridElementWidth / 2, py + canvas->gridElementHeight / 2);
-    displayCanvasFillStrokeTriangle(canvas, 0, 6, 5, -6, -5, -6);
+
+    // Main triangle
+    displayCanvasFillStrokeTriangle(canvas, 0, top, width, bottom, -width, bottom);
+    // Inset triangle
     displayCanvasSetFillColor(canvas, DISPLAY_CANVAS_COLOR_TRANSPARENT);
-    displayCanvasFillStrokeTriangle(canvas, 0, -2, 6, -7, -6, -7);
-    displayCanvasMoveToPoint(canvas, 6, -7);
-    displayCanvasSetStrokeColor(canvas, DISPLAY_CANVAS_COLOR_TRANSPARENT);
-    displayCanvasStrokeLineToPoint(canvas, -6, -7);
+    displayCanvasFillTriangle(canvas, 0, topInset, width + 1, bottom - 1, -width, bottom - 1);
+    // Draw bottom strokes of the triangle
+    displayCanvasMoveToPoint(canvas, -width, bottom - 1);
+    displayCanvasStrokeLineToPoint(canvas, 0, topInset);
+    displayCanvasStrokeLineToPoint(canvas, width, bottom - 1);
 }
 
 static void osdDrawArtificialHorizonLevelLine(displayCanvas_t *canvas, int width, int pos, int margin)

src/main/io/osd_canvas.h

@@ -33,7 +33,7 @@ typedef struct displayCanvas_s displayCanvas_t;
 typedef struct osdDrawPoint_s osdDrawPoint_t;
 
 void osdCanvasDrawVario(displayPort_t *display, displayCanvas_t *canvas, const osdDrawPoint_t *p, float zvel);
-void osdCanvasDrawDirArrow(displayPort_t *display, displayCanvas_t *canvas, const osdDrawPoint_t *p, float degrees, bool eraseBefore);
+void osdCanvasDrawDirArrow(displayPort_t *display, displayCanvas_t *canvas, const osdDrawPoint_t *p, float degrees);
 void osdCanvasDrawArtificialHorizon(displayPort_t *display, displayCanvas_t *canvas, const osdDrawPoint_t *p, float pitchAngle, float rollAngle);
 void osdCanvasDrawHeadingGraph(displayPort_t *display, displayCanvas_t *canvas, const osdDrawPoint_t *p, int heading);
 bool osdCanvasDrawSidebars(displayPort_t *display, displayCanvas_t *canvas);

src/main/io/osd_common.c

@@ -88,17 +88,14 @@ void osdDrawVario(displayPort_t *display, displayCanvas_t *canvas, const osdDraw
 #endif
 }
 
-void osdDrawDirArrow(displayPort_t *display, displayCanvas_t *canvas, const osdDrawPoint_t *p, float degrees, bool eraseBefore)
+void osdDrawDirArrow(displayPort_t *display, displayCanvas_t *canvas, const osdDrawPoint_t *p, float degrees)
 {
-#if !defined(USE_CANVAS)
-    UNUSED(eraseBefore);
-#endif
     uint8_t gx;
     uint8_t gy;
 
 #if defined(USE_CANVAS)
     if (canvas) {
-        osdCanvasDrawDirArrow(display, canvas, p, degrees, eraseBefore);
+        osdCanvasDrawDirArrow(display, canvas, p, degrees);
     } else {
 #endif
         osdDrawPointGetGrid(&gx, &gy, display, canvas, p);

src/main/io/osd_common.h

@@ -76,7 +76,7 @@ void osdDrawVario(displayPort_t *display, displayCanvas_t *canvas, const osdDraw
 // Draws an arrow at the given point, where 0 degrees points to the top of the viewport and
 // positive angles result in clockwise rotation. If eraseBefore is true, the rect surrouing
 // the arrow will be erased first (need for e.g. the home arrow, since it uses multiple symbols)
-void osdDrawDirArrow(displayPort_t *display, displayCanvas_t *canvas, const osdDrawPoint_t *p, float degrees, bool eraseBefore);
+void osdDrawDirArrow(displayPort_t *display, displayCanvas_t *canvas, const osdDrawPoint_t *p, float degrees);
 void osdDrawArtificialHorizon(displayPort_t *display, displayCanvas_t *canvas, const osdDrawPoint_t *p, float rollAngle, float pitchAngle);
 // Draws a heading graph with heading given as 0.1 degree steps i.e. [0, 3600). It uses 9 horizontal
 // grid slots.