Why is the dial drawn on my display turning in the wrong direction? [Math]

i have pretty simple function set display dial on 128*64 oled display. it's circle line drawn center edge @ specific angle. have displaying position of stepper motor, it's turning wrong way , can't figure out why.

code: [select]


void drawdial(uint8_t radius, double angle, uint8_t h, uint8_t k) {
  uint8_t x, y;

  x = radius * cos(angle) + h;  // problem occurs these two
  y = radius * sin(angle) + k;   // these endpoints of line
 
  display.drawcircle(h, k, radius, white);    // (center x, center y, radius, color)
  display.drawline(h, k, x, y, white);         // (x1, y1, x2, y2, color)
}



an angle goes function can range 0 2pi. @ moment it's receiving angle changes 0 pi, should start x = radius + h , y = 0 + k, 3 o'clock, , start here. should rotate counter clockwise move toward pi.

for example, r = 20, angle = 0, h = 64, k = 32:
a circle of radius 20 drawn in center of screen arrow pointing 3 o'clock.

x = 20cos(0)+64 = 84
y = 20sin(0) +32 = 32

here's graph it's easier visualize. scroll variable see mean.

but trouble happens when move toward pi, r = 20, angle = pi/2, h = 64, k = 32:

x = 20cos(pi/2)+64 = 64
y = 20sin(pi/2) +32 = 52

these (x,y) coordinates should above center on top, instead it's drawn @ bottom. causing dial rotate in opposite direction should.

what's this?

sorry, answered own question. realized display coordinates start @ top left, not bottom left! y axis inverted needed change y = rcos(a)+k y = -rcos(a)+k adjust that.

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