问题描述
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,并将此旋转后的位图传递给opengl着色器代码。但是生成的图像似乎像下面那样隐藏/剪切了旋转的部分。旋转时是否需要对其视口进行任何更改?还是用着色器代码本身旋转图像好?
public void DrawImage(int image,int glcontrolWidth,int glcontrolHeight,Matrix4 **transformMatrix**)
{
GL.Viewport(new Rectangle(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,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,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);
}
解决方法
不要旋转图像,而是旋转和缩放顶点坐标。
将转换矩阵添加到顶点着色器:
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);
}
获取变换矩阵统一形式(``u_transform'')的位置(在程序链接之后)。
int transformLocation = GL.GetUniformLocation(program,"u_transform");
根据角度计算比例尺:
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);
定义一个缩放矩阵并考虑纵横比来旋转图像:
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);
在程序安装后(GL.UseProgram
之后)设置矩阵统一:
GL.UniformMatrix4(transformLocation,false,ref transformMatrix);