doue1925
2017-06-27 22:20
浏览 101
已采纳

为什么golang gomobile基本示例为vec4属性设置3浮点大小?

Golang gomobile basic example [1] uses VertexAttribPointer to set 3 x FLOATS per vertex.

However the vertex shader attribute type is vec4. Shouldn't it be vec3?

Why?

Within render loop:

glctx.VertexAttribPointer(position, coordsPerVertex, gl.FLOAT, false, 0, 0)

Triangle data:

var triangleData = f32.Bytes(binary.LittleEndian,
    0.0, 0.4, 0.0, // top left
    0.0, 0.0, 0.0, // bottom left
    0.4, 0.0, 0.0, // bottom right
)

Constant declaration:

const (
    coordsPerVertex = 3
    vertexCount     = 3
)

In vertex shader:

attribute vec4 position;

[1] gomobile basic example: https://github.com/golang/mobile/blob/master/example/basic/main.go

图片转代码服务由CSDN问答提供 功能建议

Golang gomobile基本示例[1]使用VertexAttribPointer为每个顶点设置3个FLOATS。 \ n

但是,顶点着色器属性类型为vec4。 应该不是vec3吗?

为什么?

在渲染循环内:

  glctx  .VertexAttribPointer(位置,coordsPerVertex,gl.FLOAT,false,0,0)
   
 
 

三角形数据:

  var triangleData = f32.Bytes(binary.LittleEndian,
 0.0,0.4,0.0,//左上角
 0.0,0.0,0.0,//左下角
 0.4,0.0,0.0,//右下角
  )
   
 
 

常量声明:

  const(
 coordsPerVertex = 3 
 vertexCount = 3 
)  
   
 
 

在顶点着色器中:

 属性vec4位置; 
   \  n 
 

[1] gomobile基本示例: https ://github.com/golang/mobile/blob/master/example/basic/main.go

  • 写回答
  • 好问题 提建议
  • 关注问题
  • 收藏
  • 邀请回答

1条回答 默认 最新

  • doujinge9648 2017-06-28 20:21
    已采纳

    Vertex attributes are conceptually always 4 component vectors. There is no requirement that the number of components you use in the shader and the one you set up for the attribute pointer have to match. If your array has more components than your shader consumes, the additional components are just ignored. If your array supplies less components, the attribute is filled to a vector of the form (0,0,0,1) (which makes sense for homogeneous position vectors as well as RGBA colors).

    In the usual case, you want w=1 for every input position anyway, there is no need to store that in an array. But you usually need the full 4D form when applying the transformation matrices (or even when directly forwarding the value as gl_Position). So your shader could conceptually do

    in vec3 pos;
    gl_Position=vec4(pos,1);
    

    but that would be equivalent of just writing

    in vec4 pos;
    gl_Position=pos;
    
    已采纳该答案
    评论
    解决 无用
    打赏 举报