什么是OpenGL函数gluOrtho2d
的现代等效版本?我收到了clang的弃用警告。我认为我需要编写某种顶点着色器?它应该长什么样子?
什么是OpenGL函数gluOrtho2d
的现代等效版本?我收到了clang的弃用警告。我认为我需要编写某种顶点着色器?它应该长什么样子?
void TestDraw(){
// create a vertex buffer (This is a buffer in video memory)
GLuint my_vertex_buffer;
glGenBuffers(1 /*ask for one buffer*/, &my_vertex_buffer);
const float a_2d_triangle[] =
{
200.0f, 10.0f,
10.0f, 200.0f,
400.0f, 200.0f
};
// GL_ARRAY_BUFFER indicates we're using this for
// vertex data (as opposed to things like feedback, index, or texture data)
// so this call says use my_vertex_data as the vertex data source
// this will become relevant as we make draw calls later
glBindBuffer(GL_ARRAY_BUFFER, my_vertex_buffer);
// allocate some space for our buffer
glBufferData(GL_ARRAY_BUFFER, 4096, NULL, GL_DYNAMIC_DRAW);
// we've been a bit optimistic, asking for 4k of space even
// though there is only one triangle.
// the NULL source indicates that we don't have any data
// to fill the buffer quite yet.
// GL_DYNAMIC_DRAW indicates that we intend to change the buffer
// data from frame-to-frame.
// the idea is that we can place more than 3(!) vertices in the
// buffer later as part of normal drawing activity
// now we actually put the vertices into the buffer.
glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(a_2d_triangle), a_2d_triangle);
第二部分:顶点数组对象:
我们需要定义 my_vertex_array 中包含的数据结构。这个状态是包含在一个顶点数组对象(VAO)中的。在现代OpenGL中,至少需要一个VAO。
GLuint my_vao;
glGenVertexArrays(1, &my_vao);
//lets use the VAO we created
glBindVertexArray(my_vao);
// now we need to tell the VAO how the vertices in my_vertex_buffer
// are structured
// our vertices are really simple: each one has 2 floats of position data
// they could have been more complicated (texture coordinates, color --
// whatever you want)
// enable the first attribute in our VAO
glEnableVertexAttribArray(0);
// describe what the data for this attribute is like
glVertexAttribPointer(0, // the index we just enabled
2, // the number of components (our two position floats)
GL_FLOAT, // the type of each component
false, // should the GL normalize this for us?
2 * sizeof(float), // number of bytes until the next component like this
(void*)0); // the offset into our vertex buffer where this element starts
第三部分:着色器
好的,我们已经准备好了源数据,现在我们可以设置着色器,将其转换为像素。
// first create some ids
GLuint my_shader_program = glCreateProgram();
GLuint my_fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
GLuint my_vertex_shader = glCreateShader(GL_VERTEX_SHADER);
// we'll need to compile the vertex shader and fragment shader
// and then link them into a full "shader program"
// load one string from &my_fragment_source
// the NULL indicates that the string is null-terminated
const char* my_fragment_source = FragmentSourceFromSomewhere();
glShaderSource(my_fragment_shader, 1, &my_fragment_source, NULL);
// now compile it:
glCompileShader(my_fragment_shader);
// then check the result
GLint compiled_ok;
glGetShaderiv(my_fragment_shader, GL_COMPILE_STATUS, &compiled_ok);
if (!compiled_ok){ printf("Oh Noes, fragment shader didn't compile!\n"); }
else{
glAttachShader(my_shader_program, my_fragment_shader);
}
// and again for the vertex shader
const char* my_vertex_source = VertexSourceFromSomewhere();
glShaderSource(my_vertex_shader, 1, &my_vertex_source, NULL);
glCompileShader(my_vertex_shader);
glGetShaderiv(my_vertex_shader, GL_COMPILE_STATUS, &compiled_ok);
if (!compiled_ok){ printf("Oh Noes, vertex shader didn't compile!\n"); }
else{
glAttachShader(my_shader_program, my_vertex_shader);
}
//finally, link the program, and set it active
glLinkProgram(my_shader_program);
glUseProgram(my_shader_program);
第四部分:在屏幕上绘制图形
//get the screen size
float my_viewport[4];
glGetFloatv(GL_VIEWPORT, my_viewport);
//now create a projection matrix
float my_proj_matrix[16];
MyOrtho2D(my_proj_matrix, 0.0f, my_viewport[2], my_viewport[3], 0.0f);
//"uProjectionMatrix" refers directly to the variable of that name in
// shader source
GLuint my_projection_ref =
glGetUniformLocation(my_shader_program, "uProjectionMatrix");
// send our projection matrix to the shader
glUniformMatrix4fv(my_projection_ref, 1, GL_FALSE, my_proj_matrix );
//clear the background
glClearColor(0.3, 0.4, 0.4, 1.0);
glClear(GL_COLOR_BUFFER_BIT| GL_DEPTH_BUFFER_BIT);
// *now* after that tiny setup, we're ready to draw the best 24 bytes of
// vertex data ever.
// draw the 3 vertices starting at index 0, interpreting them as triangles
glDrawArrays(GL_TRIANGLES, 0, 3);
// now just swap buffers however your window manager lets you
}
就是这样了!
... 除了实际的操作外
着色器(Shaders)
我到这个点有些疲倦了,因此注释有点少。如果您需要澄清任何事情,请告诉我。
const char* VertexSourceFromSomewhere()
{
return
"#version 330\n"
"layout(location = 0) in vec2 inCoord;\n"
"uniform mat4 uProjectionMatrix;\n"
"void main()\n"
"{\n"
" gl_Position = uProjectionMatrix*(vec4(inCoord, 0, 1.0));\n"
"}\n";
}
const char* FragmentSourceFromSomewhere()
{
return
"#version 330 \n"
"out vec4 outFragColor;\n"
"vec4 DebugMagenta(){ return vec4(1.0, 0.0, 1.0, 1.0); }\n"
"void main() \n"
"{\n"
" outFragColor = DebugMagenta();\n"
"}\n";
}
你实际提出的问题:正交投影
如注所述,实际的数学内容直接来自维基百科。
void MyOrtho2D(float* mat, float left, float right, float bottom, float top)
{
// this is basically from
// http://en.wikipedia.org/wiki/Orthographic_projection_(geometry)
const float zNear = -1.0f;
const float zFar = 1.0f;
const float inv_z = 1.0f / (zFar - zNear);
const float inv_y = 1.0f / (top - bottom);
const float inv_x = 1.0f / (right - left);
//first column
*mat++ = (2.0f*inv_x);
*mat++ = (0.0f);
*mat++ = (0.0f);
*mat++ = (0.0f);
//second
*mat++ = (0.0f);
*mat++ = (2.0*inv_y);
*mat++ = (0.0f);
*mat++ = (0.0f);
//third
*mat++ = (0.0f);
*mat++ = (0.0f);
*mat++ = (-2.0f*inv_z);
*mat++ = (0.0f);
//fourth
*mat++ = (-(right + left)*inv_x);
*mat++ = (-(top + bottom)*inv_y);
*mat++ = (-(zFar + zNear)*inv_z);
*mat++ = (1.0f);
}
zNear
的值为**-1.0,而zFar
的值为1.0**。理论上说,对于正交投影,可以使用任何一组非零值,但通常zNear
<zFar
。如果在投影矩阵中翻转了一个轴线,可能会导致多边形绕序方向出现问题。幸运的是,在这里您还通过交换bottom
和top
参数来翻转了Y轴,因此最终不会受到影响,并且左右手坐标系也不会改变。然而,这个投影矩阵将使原点(0,0)位于左上角,而不是左下角。 - Andon M. ColemangluOrtho2D
设置了一个二维正交视图区域。这相当于使用 near = -1 和 far = 1 调用 glOrtho。 - Andon M. ColemanglBindVertexArray
之后调用glBindBuffer
。 - Neil G