让我们从我所在的位置开始；
我有一个通过 FBO 生成此纹理的片段着色器。除了贝塞尔曲线，我几乎拥有我想要的所有原语。
我相当大的片段着色器：
testfrag = """//fragment
uniform float thickness; //sets beam thickness
uniform float light; //sets beam intensity
uniform vec4 lines[200]; //pairs of lines; x1, y1, x2, y2
uniform vec3 circles[200]; //circles x,y,radius
uniform vec4 ellipses[200]; //ellipses x,y,width, heightmultiplication
uniform int ellipselength = 1; //amount of ellipses
uniform int linelength = 2; //amount of linepairs
uniform int circlelength = 1; //amount of circles
uniform vec2 polygons[200]; //polygon data, points in x,y. (0,0) points used as end marker
uniform int polylength; //amount of polygons
int i; //for counter variable 1
int i2; //for counter variable 2
float mindistance = 1.0; //distance from fragment to next segment
float P2L(in vec2 p, in vec2 lp1, in vec2 lp2) //distance point to line segment
{
float squared = pow(distance(lp1, lp2), 2); //squared line length
float t = dot(p - lp1, lp2 - lp1) / squared; //relative position in parellel to line
if (t < 0.0) return distance(p, lp1); //before the line, get radius to point
if (t > 1.0) return distance(p, lp2); //after the line, get radius to point
return distance(p, lp1 + t * (lp2 - lp1)); //otherwise, get distance line to point
}
float P2C(in vec2 p, in vec3 circle) //point to circle
{
return abs(distance(p, circle.xy)-circle.z); //euclidian distance - radius
}
float P2E(in vec2 p, in vec4 ellipse) //point to ellipse
{
return abs(sqrt(pow(p.x-ellipse.x,2) + pow((p.y-ellipse.y)/ellipse.w, 2)) -ellipse.z); // similar to circle, with factor on height
}
bool PinPoly(in vec2 p, in int start, in int len) //test if point in polygon
{
int i, j;
bool c = false;
for (i = start, j = len-1+start; i < len+start; j = i++) {
if ( ((polygons[i].y>p.y) != (polygons[j].y>p.y)) &&
(p.x < (polygons[j].x-polygons[i].x) * (p.y-polygons[i].y) / (polygons[j].y-polygons[i].y) + polygons[i].x) )
c = !c;
}
return c;
} //balls if I know how this works
void main()
{
vec2 pos = gl_TexCoord[0].xy; // get position on fbo
for (i = 0; i < linelength; i++) //test lines
{
mindistance = min(mindistance, P2L(pos, lines[i].xy, lines[i].zw));
}
for (i = 0; i < circlelength; i++) //test circles
{
mindistance = min(mindistance, P2C(pos, circles[i]));
}
for (i = 0; i < ellipselength; i++) //test ellipses
{
mindistance = min(mindistance, P2E(pos, ellipses[i]));
}
i = 1;
int first;
while (i < polylength) //test polygons
{
//first for line segments
first = i-1;
while (polygons[i] != (0.0, 0.0))
{
mindistance = min(mindistance, P2L(pos, polygons[i-1], polygons[i]));
i++;
}
mindistance = min(mindistance, P2L(pos, polygons[i-1], polygons[first]));
if (PinPoly(pos, first, i-first)) //then test if it is inside a polygon
{
mindistance = 0.0;
}
i += 2; //jump over the (0,0) vec2
}
gl_FragColor = light*(1.0/thickness)*(thickness-mindistance).xxxx; //set color of fragment
}
"""
在 pyglet 环境中大致这样调用：
def on_draw(self):
if not self.inited:
vert = shader.Shader(shader.texvertex)
frag = shader.Shader(shader.testfrag)
self.TexProgram = shader.Program([vert, frag])
with self.TexProgram:
self.TexProgram["lines[0]"] = (0.25, 0.5, 0.75, 0.5)
self.TexProgram["lines[1]"] = (0.0, 0.0, 1.0, 1.0)
self.TexProgram["circles[0]"] = (0.5, 0.5, 0.1)
self.TexProgram["ellipses[0]"] = (0.75, 0.25, 0.1, 2.0) #x,y, width, multiplicator on height
self.TexProgram["polygons[0]"] = (0.1, 0.9)
self.TexProgram["polygons[1]"] = (0.2, 0.9)
self.TexProgram["polygons[2]"] = (0.2, 1)
self.TexProgram["polygons[3]"] = (0.1, 1)
self.TexProgram["polygons[4]"] = (0,0)
self.TexProgram["polygons[5]"] = (0.1, 0.1)
self.TexProgram["polygons[6]"] = (0.2, 0.1)
self.TexProgram["polygons[7]"] = (0.2, 0.2)
self.TexProgram["polygons[8]"] = (0.1, 0.2)
self.TexProgram["polygons[9]"] = (0,0)
self.TexProgram["polylength"] = 8
self.TexProgram["light"] = 1.05
self.TexProgram["thickness"] = 0.02
self.inited = True
self.clear()
else:
with self.TexProgram:
self.fbo.bind_texture()
self.fbo.clear()
t = (0.0, 0.0, 1.0, 0.0, 1.0, 1.0, 0.0, 1.0)
x1 = 0
x2 = w
y1 = 0
y2 = h
glColor4d(1,1,1,1)
glEnable (GL_TEXTURE_2D)
glBegin(GL_QUADS)
glTexCoord2d(t[0], t[1]); glVertex2d(x1, y1)
glTexCoord2d(t[2], t[3]); glVertex2d(x2, y1)
glTexCoord2d(t[4], t[5]); glVertex2d(x2, y2)
glTexCoord2d(t[6], t[7]); glVertex2d(x1, y2)
glEnd()
贝塞尔曲线通常有 3 个以上的点，一切都在 2D 空间中。在我看来，有两种方法可以解决这个问题。
1：
Generate points on curve.
get closest curve point.
generate points around curve point.
get closest point of those.
rince and repeat last steps until satisfactory precision is reached.
2：想出一个公式/算法来解析距离。我尝试了这个，但没有找到任何数量的贝塞尔曲线点的解决方案，只有一个恒定的数量。
我更喜欢第二种方法的解决方案。我可以自己想出第一种方法的解决方案，但如果有人知道任何资源来查找它，这样我就不会浪费时间了，无论如何都会有所帮助。