我从这里实现了 Xiaolin Wu 圆算法:https://create.stephan-brumme.com/antialiased-circle/在 C++ 中:
float radiusX = endRadius;
float radiusY = endRadius;
float radiusX2 = radiusX * radiusX;
float radiusY2 = radiusY * radiusY;
float maxTransparency = 127;
float quarter = roundf(radiusX2 / sqrtf(radiusX2 + radiusY2));
for(float _x = 0; _x <= quarter; _x++) {
float _y = radiusY * sqrtf(1 - _x * _x / radiusX2);
float error = _y - floorf(_y);
float transparency = roundf(error * maxTransparency);
int alpha = transparency;
int alpha2 = maxTransparency - transparency;
setPixel4(x, y, _x, floorf(_y), r, g, b, alpha, data, areasData, false);
setPixel4(x, y, _x, floorf(_y) - 1, r, g, b, alpha2, data, areasData, false);
}
quarter = roundf(radiusY2 / sqrtf(radiusX2 + radiusY2));
for(float _y = 0; _y <= quarter; _y++) {
float _x = radiusX * sqrtf(1 - _y * _y / radiusY2);
float error = _x - floorf(_x);
float transparency = roundf(error * maxTransparency);
int alpha = transparency;
int alpha2 = maxTransparency - transparency;
setPixel4(x, y, floorf(_x), _y, r, g, b, alpha, data, areasData, false);
setPixel4(x, y, floorf(_x) - 1, _y, r, g, b, alpha2, data, areasData, false);
}
x,y 为圆心坐标。
在我看来它看起来不错:
但是,我需要填充圆圈。也许我错了,但我开发了一个简单的算法:从 1 迭代到半径并画一个圆。它看起来像这样:
奇怪。所以,为了解决这个问题,我还将透明度设置为最大,直到我到达最后一个半径(所以它是一个外圆):
如您所见,外层和其他层之间有奇怪的孔。我试过制作两个外层和类似的东西,但没有得到正确的结果。
这是代码的最终版本:
for(int cradius = startRadius; cradius <= endRadius; cradius++) {
bool last = cradius == endRadius;
float radiusX = cradius;
float radiusY = cradius;
float radiusX2 = radiusX * radiusX;
float radiusY2 = radiusY * radiusY;
float maxTransparency = 127;
float quarter = roundf(radiusX2 / sqrtf(radiusX2 + radiusY2));
for(float _x = 0; _x <= quarter; _x++) {
float _y = radiusY * sqrtf(1 - _x * _x / radiusX2);
float error = _y - floorf(_y);
float transparency = roundf(error * maxTransparency);
int alpha = transparency;
int alpha2 = maxTransparency - transparency;
if(!last) {
alpha = maxTransparency;
alpha2 = maxTransparency;
}
setPixel4(x, y, _x, floorf(_y), r, g, b, alpha, data, areasData, false);
setPixel4(x, y, _x, floorf(_y) - 1, r, g, b, alpha2, data, areasData, false);
}
quarter = roundf(radiusY2 / sqrtf(radiusX2 + radiusY2));
for(float _y = 0; _y <= quarter; _y++) {
float _x = radiusX * sqrtf(1 - _y * _y / radiusY2);
float error = _x - floorf(_x);
float transparency = roundf(error * maxTransparency);
int alpha = transparency;
int alpha2 = maxTransparency - transparency;
if(!last) {
alpha = maxTransparency;
alpha2 = maxTransparency;
}
setPixel4(x, y, floorf(_x), _y, r, g, b, alpha, data, areasData, false);
setPixel4(x, y, floorf(_x) - 1, _y, r, g, b, alpha2, data, areasData, false);
}
}
我该如何解决这个问题?
编辑:
因为我不能使用 flood-fill 来填充圆圈(我绘制的区域可能不是单色背景,我需要混合这些颜色)我实现了简单的方法来连接点和线:
我在 setPixel4 方法中添加了 2 个 drawLine 调用:
void setPixel4(int x, int y, int deltaX, int deltaY, int r, int g, int b, int a, unsigned char* data, unsigned char* areasData, bool blendColor) {
drawLine(x - deltaX, y - deltaY, x + deltaX, y + deltaY, r, g, b, 127, data, areasData); //maxTransparency
drawLine(x + deltaX, y - deltaY, x - deltaX, y + deltaY, r, g, b, 127, data, areasData); //maxTransparency
setPixelWithCheckingArea(x + deltaX, y + deltaY, r, g, b, a, data, areasData, blendColor);
setPixelWithCheckingArea(x - deltaX, y + deltaY, r, g, b, a, data, areasData, blendColor);
setPixelWithCheckingArea(x + deltaX, y - deltaY, r, g, b, a, data, areasData, blendColor);
setPixelWithCheckingArea(x - deltaX, y - deltaY, r, g, b, a, data, areasData, blendColor);
}
它看起来和第三张图一模一样。我认为里面的这些白色像素是由外圈(来自 xiaolin wu 算法)本身引起的。
编辑 2:
感谢@JaMiT,我改进了我的代码并且它适用于一个圆圈,但是当我有更多的相互重叠时失败了。一、新代码:
void drawFilledCircle(int x, int y, int startRadius, int endRadius, int r, int g, int b, int a, unsigned char* data, unsigned char* areasData, int startAngle, int endAngle, bool blendColor) {
assert(startAngle <= endAngle);
assert(startRadius <= endRadius);
dfBufferCounter = 0;
for(int i = 0; i < DRAW_FILLED_CIRCLE_BUFFER_SIZE; i++) {
drawFilledCircleBuffer[i] = -1;
}
for(int cradius = endRadius; cradius >= startRadius; cradius--) {
bool last = cradius == endRadius;
bool first = cradius == startRadius && cradius != 0;
float radiusX = cradius;
float radiusY = cradius;
float radiusX2 = radiusX * radiusX;
float radiusY2 = radiusY * radiusY;
float maxTransparency = 127;
float quarter = roundf(radiusX2 / sqrtf(radiusX2 + radiusY2));
for(float _x = 0; _x <= quarter; _x++) {
float _y = radiusY * sqrtf(1 - _x * _x / radiusX2);
float error = _y - floorf(_y);
float transparency = roundf(error * maxTransparency);
int alpha = last ? transparency : maxTransparency;
int alpha2 = first ? maxTransparency - transparency : maxTransparency;
setPixel4(x, y, _x, floorf(_y), r, g, b, alpha, cradius, endRadius, data, areasData, blendColor);
setPixel4(x, y, _x, floorf(_y) - 1, r, g, b, alpha2, cradius, endRadius, data, areasData, blendColor);
}
quarter = roundf(radiusY2 / sqrtf(radiusX2 + radiusY2));
for(float _y = 0; _y <= quarter; _y++) {
float _x = radiusX * sqrtf(1 - _y * _y / radiusY2);
float error = _x - floorf(_x);
float transparency = roundf(error * maxTransparency);
int alpha = last ? transparency : maxTransparency;
int alpha2 = first ? maxTransparency - transparency : maxTransparency;
setPixel4(x, y, floorf(_x), _y, r, g, b, alpha, cradius, endRadius, data, areasData, blendColor);
setPixel4(x, y, floorf(_x) - 1, _y, r, g, b, alpha2, cradius, endRadius, data, areasData, blendColor);
}
}
}
在 setPixel4 中没有调用 drawLine 它看起来像这样:
我改进了 setPixel4 方法以避免再次重绘相同的像素:
void setPixel4(int x, int y, int deltaX, int deltaY, int r, int g, int b, int a, int radius, int maxRadius, unsigned char* data, unsigned char* areasData, bool blendColor) {
for(int j = 0; j < 4; j++) {
int px, py;
if(j == 0) {
px = x + deltaX;
py = y + deltaY;
} else if(j == 1) {
px = x - deltaX;
py = y + deltaY;
} else if(j == 2) {
px = x + deltaX;
py = y - deltaY;
} else if(j == 3) {
px = x - deltaX;
py = y - deltaY;
}
int index = (px + (img->getHeight() - py - 1) * img->getWidth()) * 4;
bool alreadyInBuffer = false;
for(int i = 0; i < dfBufferCounter; i++) {
if(i >= DRAW_FILLED_CIRCLE_BUFFER_SIZE) break;
if(drawFilledCircleBuffer[i] == index) {
alreadyInBuffer = true;
break;
}
}
if(!alreadyInBuffer) {
if(dfBufferCounter < DRAW_FILLED_CIRCLE_BUFFER_SIZE) {
drawFilledCircleBuffer[dfBufferCounter++] = index;
}
setPixelWithCheckingArea(px, py, r, g, b, a, data, areasData, blendColor);
}
}
}
然后,最后:
这几乎是完美的。但是,我花了很多时间来摆脱这个白色轮廓,但我做不到。
最佳答案
因为您将圆圈离散化,所以一些像素必然会丢失。您获得的图片显示了众所周知的莫尔效应。
最好的解决方案是使用任何洪水填充算法或综合在同一水平线(如果您愿意,也可以是垂直线)上的圆点之间画线的简单算法。
关于c++ - Xiaolin Wu 圆算法渲染圆里面有洞,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/54594822/