为 OpenGL 中的 3d 锥体设置颜色

Question

I'm learning about OpenGL and I use C# for it. I want to have a red cone and an opportunity to change its transparency.

This is what I do:

Gl.glColor4f(255, 0, 0, alpha);
Glut.glutSolidCone(cone.Radius, cone.Height, cone.Slices, cone.Stacks);

As a result I get something like this:

So it really is a cone but the color is just white (alpha = 1 when ran).

How to achieve the red color with an ability to make it transparent?

Answer 1

Thank you for your replies, Finally: got a solution:

Gl.glEnable(Gl.GL_BLEND);
Gl.glBlendFunc(Gl.GL_SRC_ALPHA, Gl.GL_ONE_MINUS_SRC_ALPHA);
Gl.glEnable(Gl.GL_COLOR_MATERIAL);
Gl.glColor4f(255, 0, 0, alpha);
Glut.glutSolidCone(cone.Radius, cone.Height, cone.Slices, cone.Stacks);

So I have a Scroll Bar to change alpha parameter and the cone does change its transparency. By the way, 255 and 1 works the same (solid red color)

Answer 2

I hope this answer helps also.

The main render class, sets up the camera view and renders all the lights, and then renders all the objects in the scene:

 public void RenderOnView(GLControl control) { control.MakeCurrent(); var camera = views[control]; GL.Clear(ClearBufferMask.ColorBufferBit|ClearBufferMask.DepthBufferBit); GL.Disable(EnableCap.CullFace); GL.BlendFunc(BlendingFactorSrc.SrcAlpha, BlendingFactorDest.OneMinusSrcAlpha); camera.LookThrough(); if (EnableLights) { GL.LightModel(LightModelParameter.LightModelAmbient, new[] { 0.2f, 0.2f, 0.2f, 1f }); GL.LightModel(LightModelParameter.LightModelLocalViewer, 1); GL.Enable(EnableCap.Lighting); foreach (var light in lights) { light.Render(); } } else { GL.Disable(EnableCap.Lighting); GL.ShadeModel(ShadingModel.Flat); } GL.Enable(EnableCap.LineSmooth); // This is Optional GL.Enable(EnableCap.Normalize); // These is critical to have GL.Enable(EnableCap.RescaleNormal); for (int i = 0; i<objects.Count; i++) { GL.PushMatrix(); objects[i].Render(); GL.PopMatrix(); } control.SwapBuffers(); }