如何对纹理执行HSL变换?

这是相当复杂的,如果你是新的着色器和FBO的它将需要一些时间来理解它。下面是一些最小的,未经测试的OpenGL代码 Danvil's answer . 漏掉了错误检查;这已经够复杂了。如果多次调用此函数,则应保留在此代码中创建的任何或所有对象。

VilleK's answer 在CPU上运行要容易得多。。。

// Create the target texture object.
GLuint target;
glGenTextures(1, &target);

// Bind the target texture.
glBindTexture(GL_TEXTURE_2D, target);

// Allocate texture memory. width and height must be the size of the original texture.
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);

// Create a framebuffer object.
GLuint fbo;
glGenFramebuffers(1, &fbo);

// Bind the framebuffer object.
glBindFramebuffer(GL_FRAMEBUFFER, fbo);

// Attach the target texture as the render target.
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, target, 0);

// Check framebuffer status.
if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
    throw "Framebuffer incomplete.";

// Create fragment shader to do the transformation.
GLuint frag = glCreateShader(GL_FRAGMENT_SHADER);

// Set the shader's source code.
char const *source =
    "uniform sampler2D input;\n"
    "uniform float hShift, sMult, lMult;\n"
    "void main() {\n"
    "    vec4 color = texture2D(input, gl_FragCoord.xy);\n"
    "    /* Do your HSL transformations here... */\n"
    "    gl_FragColor = color;\n"
    "}\n";
glShaderSource(frag, 1, &source, 0);

// Compile the shader.
glCompileShader(frag);

// Check compilation result. Here, you probably want to use glGetShaderInfoLog() to get any compilation errors.
GLint status;
glGetShader(frag, GL_COMPILE_STATUS, &status);
if (status == GL_FALSE)
    throw "Shader compilation failed";

// Create the program.
GLuint program = glCreateProgram();

// Attach the shader to the program.
glAttachShader(program, frag);

// Link the program.
glLinkProgram(program);

// Check link result. Here, you probably want to use glGetProgramInfoLog() to get any link errors.
glGetProgram(program, GL_LINK_STATUS, &status);
if (status == GL_FALSE)
    throw "Program linking failed"

// Use the program for subsequent rendering.
glUseProgram(program);

// Set the values of the uniform parameters.
glUniform1i(glUniformLocation(program, "input"), 0);
glUniform1f(glUniformLocation(program, "hShift"), hShift);
glUniform1f(glUniformLocation(program, "sMult"), sMult);
glUniform1f(glUniformLocation(program, "lMult"), lMult);

// Bind the source texture to read from.
glBindTexture(GL_TEXTURE_2D, texture);

// Set up the viewport and matrices.
glPushAttrib(GL_VIEWPORT_BIT | GL_TRANSFORM_BIT);
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
glOrtho(0, 1, 0, 1, 0, 1);
glViewport(0, 0, width, height);

// Render a quad.
glBegin(GL_QUADS);
glVertex2i(0, 0);
glVertex2i(1, 0);
glVertex2i(1, 1);
glVertex2i(0, 1);
glEnd();

// Restore the matrices and viewport.
glPopMatrix();
glMatrixMode(GL_MODELVIEW);
glPopMatrix();
glPopAttrib();

// Stop using the program.
glUseProgram(0);

// Stop using the framebuffer object.
glBindFramebuffer(GL_FRAMEBUFFER, 0);

// Delete created objects.
glDeleteProgram(program);
glDeleteShader(frag);
glDeleteFramebuffers(1, &fbo);

// Optionally, delete the old, untransformed texture.
glDeleteTextures(1, &texture);

// Return the new texture.
return target;

希望有帮助。对于2.0opengl之前的版本,您需要首先加载适当的扩展,然后添加一些 EXT s和/或 ARB

如果你愿意走这条路,但没有成功,不要犹豫,发表评论,描述你遇到的问题。我很乐意帮忙!

The CG Tutorial

一旦编写了着色器,就可以用OpenGL扩展函数加载并绑定它。当您将几何体推入管道时,它将由光栅化器应用。下面是一个简单的教程,演示如何编写和使用非常基本的着色器:

Tutorial - Cg Pixel Shaders in OpenGL

  //Get copy of pixels. P is a pointer to floats (^single)
  GetMem(P,TextureHeight * TextureWidth * 4 * SizeOf(single));
  glGetTexImage(GL_TEXTURE_2D,0,GL_RGBA,GL_FLOAT,P);
  ... loop and modify pixels here. 4 float values per pixels: Red, green, blue and alpha
  //Update texture with modified pixels
  glTexImage2D(GL_TEXTURE_2D, 0, 4, TextureWidth, TextureHeight , 0, GL_RGBA, GL_FLOAT, P);
  FreeMem(P);

如果要使用字节而不是浮点,可以使用GL\u UNSIGNED\u BYTE。

使用“渲染到纹理”(render to texture):

1. 使用源纹理texRgb的大小创建新的(目标)纹理texHSL
2. 使用 orthogonal projection
3. framebuffer 并使用纹理texHSL作为渲染目标
4. 使用着色器渲染屏幕大小的四边形(可能更大)。对于着色器,使用统一的
5. reads the texture value for the currently rendered value (参见此处的答案),计算RGB->HSL转换并将HSL值写入gl\u FragColor
7. 瞧,你转换的图像是texHSL格式的