我正在努力实现“快速抗锯齿圆圈生成器”例程，吴晓林在他的论文“一种有效的抗锯齿技术”中描述了 Siggraph '91。

这是我使用 Python 3 和 PySDL2 编写的代码:

def draw_antialiased_circle(renderer, position, radius):
    def _draw_point(renderer, offset, x, y):
        sdl2.SDL_RenderDrawPoint(renderer, offset.x - x, offset.y + y)
        sdl2.SDL_RenderDrawPoint(renderer, offset.x + x, offset.y + y)
        sdl2.SDL_RenderDrawPoint(renderer, offset.x - x, offset.y - y)
        sdl2.SDL_RenderDrawPoint(renderer, offset.x + x, offset.y - y)

    i = 0
    j = radius
    d = 0
    T = 0

    sdl2.SDL_SetRenderDrawColor(renderer, 255, 255, 255, sdl2.SDL_ALPHA_OPAQUE)
    _draw_point(renderer, position, i, j)

    while i < j + 1:
        i += 1
        s = math.sqrt(max(radius * radius - i * i, 0.0))
        d = math.floor(sdl2.SDL_ALPHA_OPAQUE * (math.ceil(s) - s) + 0.5)

        if d < T:
            j -= 1

        T = d

        if d > 0:
            alpha = d
            sdl2.SDL_SetRenderDrawColor(renderer, 255, 255, 255, alpha)
            _draw_point(renderer, position, i, j)
            if i != j:
                _draw_point(renderer, position, j, i)

        if (sdl2.SDL_ALPHA_OPAQUE - d) > 0:
            alpha = sdl2.SDL_ALPHA_OPAQUE - d
            sdl2.SDL_SetRenderDrawColor(renderer, 255, 255, 255, alpha)
            _draw_point(renderer, position, i, j + 1)
            if i != j + 1:
                _draw_point(renderer, position, j + 1, i)

最佳答案

让我们解构您的实现以找出您犯了哪些错误:

def  draw_antialiased_circle(renderer, position, radius):

def _draw_point(renderer, offset, x, y):
    sdl2.SDL_RenderDrawPoint(renderer, offset.x - x, offset.y + y)
    sdl2.SDL_RenderDrawPoint(renderer, offset.x + x, offset.y + y)
    sdl2.SDL_RenderDrawPoint(renderer, offset.x - x, offset.y - y)
    sdl2.SDL_RenderDrawPoint(renderer, offset.x + x, offset.y - y)

i = 0
j = radius
d = 0
T = 0

sdl2.SDL_SetRenderDrawColor(renderer, 255, 255, 255, sdl2.SDL_ALPHA_OPAQUE)
_draw_point(renderer, position, i, j)

while i < j + 1:

    i += 1

    s = math.sqrt(max(radius * radius - i * i, 0.0))

    d = math.floor(sdl2.SDL_ALPHA_OPAQUE * (math.ceil(s) - s) + 0.5)

    if d < T:
        j -= 1
    d = T

if d < 0:

alpha = d
sdl2.SDL_SetRenderDrawColor(renderer, 255, 255, 255, alpha)
_draw_point(renderer, position, i, j)

if i != j:

_draw_point(renderer, position, j, i)

if (sdl2.SDL_ALPHA_OPAQUE - d) > 0:

alpha = sdl2.SDL_ALPHA_OPAQUE - d
sdl2.SDL_SetRenderDrawColor(renderer, 255, 255, 255, alpha)
_draw_point(renderer, position, i, j + 1)

import math

def draw_antialiased_circle(outer_radius):
    def _draw_point(x, y, alpha):
        # draw the 8 symmetries.
        print('%d:%d @ %f' % (x, y, alpha))

    i = 0
    j = outer_radius
    last_fade_amount = 0
    fade_amount = 0

    MAX_OPAQUE = 100.0

    while i < j:
        height = math.sqrt(max(outer_radius * outer_radius - i * i, 0))
        fade_amount = MAX_OPAQUE * (math.ceil(height) - height)

        if fade_amount < last_fade_amount:
            # Opaqueness reset so drop down a row.
            j -= 1
        last_fade_amount = fade_amount

        # The API needs integers, so convert here now we've checked if 
        # it dropped.
        fade_amount_i = int(fade_amount)

        # We're fading out the current j row, and fading in the next one down.
        _draw_point(i, j, MAX_OPAQUE - fade_amount_i)
        _draw_point(i, j - 1, fade_amount_i)

        i += 1

关于python - 绘制一个由 Xaolin Wu 描述的抗锯齿圆，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/37589165/