1. ellipseMode(CENTER):
- 默认模式
- ellipse(圆心x，圆心y，短轴长，长轴长)
2. ellipseMode(RADIUS):
- ellipse(圆心x，圆心y，短半轴长，长半轴长)
3. ellipseMode(CORNER):
- ellipse(左上角x，左上角y，短轴长，长轴长)
4. ellipseMode(CORNERS):
- ellipse(左上角x，左上角y，右下角x，右下角y)
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Reference:
1. https://processing.org/reference/ellipseMode_.html