使用顶点着色器时如何获得平坦的、非插值的颜色

发布于 2024-08-29 22:08:46 字数 439 浏览 11 评论 0原文

有没有办法实现这一点（OpenGL 2.1）？如果我像这样画线，

glShadeModel(GL_FLAT);
glBegin(GL_LINES);
  glColor3f(1.0, 1.0, 0.0);
  glVertex3fv(bottomLeft);
  glVertex3fv(topRight);

  glColor3f(1.0, 0.0, 0.0);
  glVertex3fv(topRight);
  glVertex3fv(topLeft);
  .
  .
  (draw a square)
  .
  .
glEnd();

我会得到所需的结果（每个边缘有不同的颜色），但我希望能够计算着色器中的片段值。如果我在设置着色器程序后执行相同的操作，我总是会在顶点之间获得插值颜色。有办法解决这个问题吗？（如果我能使用四边形得到相同的结果，那就更好了）

谢谢

原文

Is there a way to achieve this (OpenGL 2.1)? If I draw lines like this

glShadeModel(GL_FLAT);
glBegin(GL_LINES);
  glColor3f(1.0, 1.0, 0.0);
  glVertex3fv(bottomLeft);
  glVertex3fv(topRight);

  glColor3f(1.0, 0.0, 0.0);
  glVertex3fv(topRight);
  glVertex3fv(topLeft);
  .
  .
  (draw a square)
  .
  .
glEnd();

I get the desired result (a different colour for each edge) but I want to be able to calculate the fragment values in a shader. If I do the same after setting up my shader program I always get interpolated colors between vertices. Is there a way around this? (would be even better if I could get the same results using quads)

Thanks

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不乱于心 2024-09-05 22:08:46

如果您不希望基元内的顶点属性之间进行插值（例如，您的情况下线段中的颜色），您将需要传递相同的颜色两次，因此最终会复制您的几何图形：

 v0             v1          v2
 x--------------x-----------x

（v0 由结构体 p0 组成以及 p1 和 c1 的 c0、v1 等..)

对于使用颜色插值绘制线条：

glBegin(GL_LINES);
//draw first segment
glColor3fv(&c0); glVertex3fv(&p0);
glColor3fv(&c1); glVertex3fv(&p1);
//draw second segment
glColor3fv(&c1); glVertex3fv(&p1);
glColor3fv(&c2); glVertex3fv(&p2);
glEnd();

对于不使用插值绘制：

glBegin(GL_LINES);
//draw first segment
glColor3fv(&c0); glVertex3fv(&p0);
glColor3fv(&c0); glVertex3fv(&p1);
//draw second segment
glColor3fv(&c1); glVertex3fv(&v1);
glColor3fv(&c1); glVertex3fv(&v2);
glEnd();

请注意，这意味着您不能再使用 GL_x_STRIP 拓扑，因为您不想共享基元内的属性。

If you don't want the interpolation between vertice attributes inside a primitive (e.g. color in a line segment in your case) you'll need to pass the same color twice, so end up duplicating your geometry:

 v0             v1          v2
 x--------------x-----------x

(v0 is made of structs p0 and c0, v1 of p1 and c1 etc..)

For drawing the line with color interpolation:

glBegin(GL_LINES);
//draw first segment
glColor3fv(&c0); glVertex3fv(&p0);
glColor3fv(&c1); glVertex3fv(&p1);
//draw second segment
glColor3fv(&c1); glVertex3fv(&p1);
glColor3fv(&c2); glVertex3fv(&p2);
glEnd();

For drawing without interpolation:

glBegin(GL_LINES);
//draw first segment
glColor3fv(&c0); glVertex3fv(&p0);
glColor3fv(&c0); glVertex3fv(&p1);
//draw second segment
glColor3fv(&c1); glVertex3fv(&v1);
glColor3fv(&c1); glVertex3fv(&v2);
glEnd();

Note this mean you can no longer use GL_x_STRIP topology, since you don't want to share attributes inside a primitive.

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