在 openTK 中旋转图像

Question

我想将 GLControl 中显示的图像旋转 10 度。为此，我使用 c# 代码旋转了位图，并将这个旋转的位图传递给 opengl 着色器代码。但是结果图像似乎像下面这样隐藏/剪切了旋转部分。我需要在旋转时对其视口进行任何更改吗？或者在着色器代码本身中旋转图像是否很好？

     public void DrawImage(int image, int glcontrolWidth, int glcontrolHeight,Matrix4 **transformMatrix**)
    {
        GL.Viewport(new Rectangle(0, 0, glcontrolWidth, glcontrolHeight));    
        GL.MatrixMode(MatrixMode.Projection);
        GL.PushMatrix();
        GL.LoadIdentity();

        GL.MatrixMode(MatrixMode.Modelview);
        GL.PushMatrix();
        GL.LoadIdentity();

        GL.Disable(EnableCap.Lighting);
        GL.Enable(EnableCap.Texture2D);

        GL.ActiveTexture(TextureUnit.Texture0);
        GL.BindTexture(TextureTarget.Texture2D, image);
        GL.Uniform1(positionLocation1, 0);

        RunShaders();
       
        GL.Disable(EnableCap.Texture2D);
        GL.PopMatrix();

        GL.MatrixMode(MatrixMode.Projection);
        GL.PopMatrix();

        GL.MatrixMode(MatrixMode.Modelview);        

    }
    public void RunShaders()
    {
        GL.UseProgram(program);
        **GL.UniformMatrix4(transformLocation, false, ref transformMatrix);**
        GL.DrawArrays(PrimitiveType.Triangles, 0, vertices.Length / 3);
        ErrorCode ec = GL.GetError();
        if (ec != 0)
            System.Console.WriteLine(ec.ToString());
        Console.Read();
    }
    public void Init()
    {
        CreateShaders();
        CreateProgram();        
        InitBuffers();
    }
    public void CreateProgram()
    {
        program = GL.CreateProgram();
        GL.AttachShader(program, vertShader);
        GL.AttachShader(program, fragShader);
        GL.LinkProgram(program);       
    }
    public void InitBuffers()
    {
        buffer = GL.GenBuffer();
        positionLocation = GL.GetAttribLocation(program, "a_position");
        positionLocation1 = GL.GetUniformLocation(program, "sTexture");
        **transformLocation = GL.GetUniformLocation(program, "u_transform");**      
        GL.EnableVertexAttribArray(positionLocation);
        GL.BindBuffer(BufferTarget.ArrayBuffer, buffer);
        GL.BufferData(BufferTarget.ArrayBuffer, (IntPtr)(vertices.Length * sizeof(float)), vertices, BufferUsageHint.StaticDraw);
        GL.VertexAttribPointer(positionLocation, 3, VertexAttribPointerType.Float, false, 0, 0);

    }
    public void CreateShaders()
    {
        /***********Vert Shader********************/
        vertShader = GL.CreateShader(ShaderType.VertexShader);
        GL.ShaderSource(vertShader, @"attribute vec3 a_position;
                                varying vec2 vTexCoord;
                           **uniform mat4 u_transform;**
                                void main() {
                                vTexCoord = (a_position.xy+1)/2 ;  
                                **gl_Position = u_transform * vec4(a_position, 1);**
                                }");
        GL.CompileShader(vertShader);

        /***********Frag Shader ****************/
        fragShader = GL.CreateShader(ShaderType.FragmentShader);
        GL.ShaderSource(fragShader, @"precision highp float;
  uniform sampler2D sTexture_2;varying vec2 vTexCoord; 
          void main ()
         {
     vec4 color = texture2D (sTexture_2, vec2(vTexCoord.x, vTexCoord.y));
     gl_FragColor =color;

   }"); GL.CompileShader(fragShader);

    }
  

Answer 1

不要旋转图像，而是旋转和缩放顶点坐标。

给顶点着色器添加一个变换矩阵：

attribute vec3 a_position;
varying vec2 vTexCoord;
uniform mat4 u_transform;

void main()
{
    vTexCoord = (a_position.xy+1)/2;
    gl_Position = u_transform * vec4(a_position, 1);
}

获取变换矩阵uniform (``u_transform') 的位置（程序链接后）。

int transformLocation = GL.GetUniformLocation(program, "u_transform");

根据角度计算比例：

double diagonal = Math.Sqrt(bmp.Width * bmp.Width + bmp.Height * bmp.Height);
double dia_angle1 = Math.Atan2(bmp.Height, bmp.Width) + angle * Math.PI / 180;
double dia_angle2 = Math.Atan2(bmp.Height, -bmp.Width) + angle * Math.PI / 180;
double rot_w = Math.Max(Math.Abs(diagonal * Math.Cos(dia_angle1)), Math.Abs(diagonal * Math.Cos(dia_angle2)));
double rot_h = Math.Max(Math.Abs(diagonal * Math.Sin(dia_angle1)), Math.Abs(diagonal * Math.Sin(dia_angle2)));
double scale = Math.Min(bmp.Width / rot_w, bmp.Height / rot_h);

定义一个变换矩阵，在考虑纵横比的情况下缩放和旋转图像：

Matrix4 transformMatrix =
    Matrix4.CreateScale((float)scale) *
    Matrix4.CreateScale(this.Width, this.Height, 1.0f) *
    Matrix4.CreateRotationZ((float)(angle * Math.PI / 180)) *
    Matrix4.CreateScale(1.0f / this.Width, 1.0f / this.Height, 1.0f);

设置矩阵统一，程序安装后（GL.UseProgram后）：

GL.UniformMatrix4(transformLocation, false, ref transformMatrix);