我正在尝试实现此处所示的线宽:
start = line start = vector(x1, y1)
end = line end = vector(x2, y2)
dir = line direction = end - start = vector(x2-x1, y2-y1)
ndir = normalized direction = dir*1.0/length(dir)
perp = perpendicular to direction = vector(dir.x, -dir.y)
nperp = normalized perpendicular = perp*1.0/length(perp)
perpoffset = nperp*w*0.5
diroffset = ndir*w*0.5
p0, p1, p2, p3 = polygon points:
p0 = start + perpoffset - diroffset
p1 = start - perpoffset - diroffset
p2 = end + perpoffset + diroffset
p3 = end - perpoffset + diroffset
我是这样实现的:
void OGLENGINEFUNCTIONS::GenerateLinePoly(const std::vector<std::vector<GLdouble>> &input, std::vector<GLfloat> &output, int width)
{
output.clear();
float temp;
float dirlen;
float perplen;
POINTFLOAT start;
POINTFLOAT end;
POINTFLOAT dir;
POINTFLOAT ndir;
POINTFLOAT perp;
POINTFLOAT nperp;
POINTFLOAT perpoffset;
POINTFLOAT diroffset;
POINTFLOAT p0, p1, p2, p3;
for(int i = 0; i < input.size() - 1; ++i)
{
start.x = input[i][0];
start.y = input[i][1];
end.x = input[i + 1][0];
end.y = input[i + 1][1];
dir.x = end.x - start.x;
dir.y = end.y - start.y;
dirlen = sqrt((dir.x * dir.x) + (dir.y * dir.y));
ndir.x = dir.x * (1.0 / dirlen);
ndir.y = dir.y * (1.0 / dirlen);
perp.x = dir.x;
perp.y = -dir.y;
perplen = sqrt((perp.x * perp.x) + (perp.y * perp.y));
nperp.x = perp.x * (1.0 / perplen);
nperp.y = perp.y * (1.0 / perplen);
perpoffset.x = nperp.x * width * 0.5;
perpoffset.y = nperp.y * width * 0.5;
diroffset.x = ndir.x * width * 0.5;
diroffset.y = ndir.y * width * 0.5;
// p0 = start + perpoffset - diroffset
//p1 = start - perpoffset - diroffset
//p2 = end + perpoffset + diroffset
// p3 = end - perpoffset + diroffset
p0.x = start.x + perpoffset.x - diroffset.x;
p0.y = start.y + perpoffset.y - diroffset.y;
p1.x = start.x - perpoffset.x - diroffset.x;
p1.y = start.y - perpoffset.y - diroffset.y;
p2.x = end.x + perpoffset.x + diroffset.x;
p2.y = end.y + perpoffset.y + diroffset.y;
p3.x = end.x - perpoffset.x + diroffset.x;
p3.y = end.y - perpoffset.y + diroffset.y;
output.push_back(p0.x);
output.push_back(p0.y);
output.push_back(p1.x);
output.push_back(p1.y);
output.push_back(p2.x);
output.push_back(p2.y);
output.push_back(p3.x);
output.push_back(p3.y);
}
}
但是现在这些线看起来是垂直的而且是错误的;它应该给我四边形来渲染,这就是我正在渲染的,但它输出的点很奇怪。我做错了吗?
谢谢
最佳答案
您计算的 perp 不正确。它应该是 (y, -x)
,而不是 (x, -y)
。我不知道这是不是唯一的错误。这个突然向我袭来。
顺便说一句,我强烈建议您定义一个有用的 vec2 类型,以及一些有用的助手,例如:
vec2 perp(vec2 v) { return vec2(v.y, -v.x); }
这样,您的代码看起来几乎与您的伪代码相同。单独操作 x
和 y
更容易出错,也更难阅读。为此目的构建一个基本类非常简单,但您最好还是找到第三方实现来避免上述错误。大多数游戏/图形/物理引擎都提供了一堆有用的类型和函数。
关于c++ - 我是否正确实现了这一点?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/2982505/