问题描述
我正在渲染球体上的一些LineLoop(行星上的边界),并希望将它们细分成更短的线,以防止长线夹入球体.例子:
I am rendering some LineLoops on a sphere (borders on a planet) and want to tessallate them into shorter lines to prevent long lines clipping into the sphere.Example:
这是我当前的源代码:C ++绘图调用:
Here is my current source code:C++ draw call:
void Border::Draw() const
{
glBindVertexArray(_vao);
glPatchParameteri(GL_PATCH_VERTICES, 2);
glDrawArrays(GL_PATCHES, 0, _size);
glBindVertexArray(0);
}
顶点着色器:
#version 400
in layout(location = 0) vec3 position;
void main()
{
gl_Position = vec4(position, 1.0);
}
镶嵌控制着色器:
#version 400
layout (vertices = 2) out;
void main()
{
if(gl_InvocationID == 0)
{
//get the distance between two points
float dist = length(gl_in[0].gl_Position - gl_in[1].gl_Position);
gl_TessLevelOuter[0] = 1;
//divide line in segments of size 1.0
gl_TessLevelOuter[1] = abs(dist);
}
gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;
}
镶嵌化评估着色器
#version 400
layout (isolines, equal_spacing) in;
uniform float planetRadius;
uniform mat4 view;
uniform mat4 projection;
void main()
{
vec4 p = mix(gl_in[0].gl_Position, gl_in[1].gl_Position, gl_TessCoord.x);
//offset point so it is on the spheres surface
p = normalize(p);
p *= planetRadius;
gl_Position = projection * view * p;
}
片段着色器:
#version 400
out vec4 outColor;
void main()
{
outColor = vec4(1.0, 1.0, 1.0, 1.0);
}
镶嵌细分似乎无法像我期望的那样工作(等值线文档也很糟糕).
The tessallation doesn't seem to work like I expect it to work (documentation on isolines is also bad).
这是我使用LineLoops和仅顶点/片段着色器绘制时的外观:
This is how it looked when I draw it with LineLoops and only Vertex/Fragment Shader:
这是我实施镶嵌处理后的样子:
and this is how it looks like after I implemented my tessallation:
这些线看起来也不是棋盘格状的,并且长度与以前相同.
The lines also do not look tessallated and have the same length as before.
问候乔尼
自己找到解决方案.在下面的答案部分中查看它.
Found the solution myself. Look in answer section below to see it.
推荐答案
我找到了解决方案.问题在于tessallation着色器无法绘制线条.因此,如果您拥有由点{p1, p2, p3, p4, p5, p6}
定义的线带,则会在以下位置之间绘制线:
p1-> p2
p3-> p4
p5-> p6
I found the solution. The problem lies within the tessallation shaders inability to draw line strips. So if you hava a line strip defined by the points {p1, p2, p3, p4, p5, p6}
it draws lines between:
p1 -> p2
p3 -> p4
p5 -> p6
我通过给着色器每个点2次来修复它,所以我的列表如下所示:{p1, p2, p2, p3, p3, p4, p4, p5, p5, p6, p6, p1}
镶嵌细分着色器创建以下行:
p1-> p2
p2-> p3
p3-> p4
p4-> p5
p5-> p6
p6-> p1
I fixed it by giving the shader every point 2 times, so my list looks like this:{p1, p2, p2, p3, p3, p4, p4, p5, p5, p6, p6, p1}
The tessallation shader creates following lines:
p1 -> p2
p2 -> p3
p3 -> p4
p4 -> p5
p5 -> p6
p6 -> p1
我的着色器现在看起来像这样:
My shaders now look like this:
TessControl:
TessControl:
#version 430
layout (vertices = 2) out;
void main()
{
if(gl_InvocationID == 0)
{
float dist = length(gl_in[0].gl_Position.xyz - gl_in[1].gl_Position.xyz);
gl_TessLevelOuter[0] = 1;
gl_TessLevelOuter[1] = dist;
}
gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;
}
TessEval:
#version 430
layout (isolines, equal_spacing) in;
uniform float planetRadius;
uniform mat4 view;
uniform mat4 projection;
void main()
{
//only interpolate and normalize xyz coordinates. Thanks to @aslg
vec3 p = mix(gl_in[0].gl_Position.xyz, gl_in[1].gl_Position.xyz, gl_TessCoord.x);
p = normalize(p);
p *= planetRadius;
gl_Position = projection * view * vec4(p, 1.0);
}
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