opengl 矩陣變換
opengl 座標系的變換如下圖：
我們給我們的圖形，設定好頂點座標後，通過model matrix 變換為世界座標，然後 view matrix相機座標，projection matrix 螢幕座標x,y ∈（-1，1）。
矩陣變換的結果是把三維的世界最終裁剪為二維的螢幕，數學的說法就是從乙個集合到另乙個集合的對映。
#include "glew.h"
#include #include "common/loadshader.h"
#include "glm.hpp"
#include "ext.hpp"
int main(void)
/* make the window's context current */
glfwmakecontextcurrent(window);
// needed in core profile
if( glewinit() != glew_ok)
// an array of 3 vectors which represents 3 vertices
static const glfloat g_vertex_buffer_data = ;
//this will identify our vertex buffer
gluint vertexbuffer;
//generate 1 buffer,put the resulting identifier in vertexbuffer
glgenbuffers(1,&vertexbuffer);
//the following commands will talk about our 'vertexbuffer' buffer
glbindbuffer(gl_array_buffer,vertexbuffer);
//give our vertices to opengl.
glbufferdata(gl_array_buffer,sizeof(g_vertex_buffer_data),g_vertex_buffer_data,gl_static_draw);
gluint programid = loadshaders("./shader/vertex.shader","./shader/fragment.shader");
gluseprogram(programid);
glclearcolor(0.0f, 0.0f, 0.4f, 0.0f);
/* loop until the user closes the window */
// projection matrix : 45° field of view, 4:3 ratio, display range : 0.1 unit 100 units
//glm::mat4 projection = glm::ortho(-4.0f/3.0f, 4.0f/3.0f, -1.0f, 1.0f, 0.1f, 100.0f);
glm::mat4 projection = glm::perspective(45.0f,4.0f/3.0f,0.1f,100.f);
glm::mat4 view = glm::lookat(
glm::vec3(4,3,3), // camera is at (4,3,3), in world space
glm::vec3(0,0,0), // and looks at the origin
glm::vec3(0,1,0) // head is up (set to 0,-1,0 to look upside-down)
);// model matrix : an identity matrix (model will be at the origin)
glm::mat4 model = glm::mat4(1.0f);
model = glm::translate(model,glm::vec3(2.0f,0.0f,0.0f));
model = glm::rotate(model,45.f,glm::vec3(0.0f,1.0f,0.0f));
model = glm::scale(model,glm::vec3(1.0f,2.0f,1.0f));
// our modelviewprojection : multiplication of our 3 matrices
glm::mat4 mvp = projection * view * model;// remember, matrix multiplication is the other way around
// get a handle for our "mvp" uniform.
// only at initialisation time.
gluint matrixid = glgetuniformlocation(programid,"mvp");
// send our transformation to the currently bound shader,
// in the "mvp" uniform
// for each model you render, since the mvp will be different (at least the m part)
gluniformmatrix4fv(matrixid,1,gl_false,&mvp[0][0]);
while (!glfwwindowshouldclose(window))
glfwterminate();
return 0;
}
然後平移，旋轉，縮放，
model = glm::translate(model,glm::vec3(2.0f,0.0f,0.0f));
model = glm::rotate(model,45.f,glm::vec3(0.0f,1.0f,0.0f));
model = glm::scale(model,glm::vec3(1.0f,2.0f,1.0f));
最後通過矩陣乘法，連線到一起。
glm::mat4 projection = glm::perspective(45.0f,4.0f/3.0f,0.1f,100.f);
glm::mat4 view = glm::lookat(
glm::vec3(4,3,3), // camera is at (4,3,3), in world space
glm::vec3(0,0,0), // and looks at the origin
glm::vec3(0,1,0) // head is up (set to 0,-1,0 to look upside-down)
);// our modelviewprojection : multiplication of our 3 matrices
glm::mat4 mvp = projection * view * model;// remember, matrix multiplication is the other way around
得到shader中變數指標
gluint matrixid = glgetuniformlocation(programid,"mvp");
將矩陣傳入shader
gluniformmatrix4fv(matrixid,1,gl_false,&mvp[0][0]);
來看shader的語法：
#version 330 core
layout(location = 0) in vec3 vertexposition_modelspace;
uniform mat4 mvp;
void main()
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