更现代的方法是通过几何着色器来实现这一点。这将适用于作为核心功能的一部分的 OpenGL 3.2 及更高版本,或者适用于扩展名为 GL_EXT_geometry_shader4 的 OpenGL 2.1。
本文有所有相关理论:Shader-Based wireframe drawing。它还提供了 GLSL 中最简单技术的示例实现。
这是我自己的尝试,基本上是他们为 OpenGL 3.3 实现的一个端口,仅限于三角形基元:
顶点着色器:(将输入替换为您用于传递顶点数据和 m、v 和 p 矩阵的任何内容)
#version 330
layout(location = 0) in vec4 position;
layout(location = 1) in mat4 mv;
out Data
{
vec4 position;
} vdata;
uniform mat4 projection;
void main()
{
vdata.position = projection * mv * position;
}
几何着色器:
#version 330
layout(triangles) in;
layout(triangle_strip, max_vertices = 3) out;
in Data
{
vec4 position;
} vdata[3];
out Data
{
noperspective out vec3 dist;
} gdata;
void main()
{
vec2 scale = vec2(500.0f, 500.0f); // scaling factor to make 'd' in frag shader big enough to show something
vec2 p0 = scale * vdata[0].position.xy/vdata[0].position.w;
vec2 p1 = scale * vdata[1].position.xy/vdata[1].position.w;
vec2 p2 = scale * vdata[2].position.xy/vdata[2].position.w;
vec2 v0 = p2-p1;
vec2 v1 = p2-p0;
vec2 v2 = p1-p0;
float area = abs(v1.x*v2.y - v1.y*v2.x);
gdata.dist = vec3(area/length(v0),0,0);
gl_Position = vdata[0].position;
EmitVertex();
gdata.dist = vec3(0,area/length(v1),0);
gl_Position = vdata[1].position;
EmitVertex();
gdata.dist = vec3(0,0,area/length(v2));
gl_Position = vdata[2].position;
EmitVertex();
EndPrimitive();
}
顶点着色器:(用您需要的任何颜色替换颜色!)
#version 330
in Data
{
noperspective in vec3 dist;
} gdata;
out vec4 outputColor;
uniform sampler2D tex;
const vec4 wireframeColor = vec4(1.0f, 0.0f, 0.0f, 1.0f);
const vec4 fillColor = vec4(1.0f, 1.0f, 1.0f, 1.0f);
void main()
{
float d = min(gdata.dist.x, min(gdata.dist.y, gdata.dist.z));
float I = exp2(-2*d*d);
outputColor = mix(fillColor, wireframeColor, I);
}