我正在尝试实现这里表示的线条粗细:
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
我已经实现了这个:
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);
}
}
但是现在线条看起来是垂直和错误的;它应该给我四边形渲染哪个是我正在渲染的,但它输出的点是奇怪的。我做错了吗?
由于
答案 0 :(得分:2)
您正在错误地计算perp。它应该是(y, -x)
,而不是(x, -y)
。我不知道这是否是唯一的错误。这个刚跳出来。
顺便说一句,我强烈建议您定义一个有用的vec2类型,并使用有用的帮助器:
vec2 perp(vec2 v) { return vec2(v.y, -v.x); }
这样,您的代码看起来与您的伪代码几乎相同。单独操作x
和y
更容易出错并且难以阅读。为此目的构建一个基本类非常简单,尽管你可能最好找到第三方实现来避免像上面那样的错误。大多数游戏/图形/物理引擎提供了许多有用的类型和功能。