opengl 渲染四边形的方式
opengl 渲染四边形的方式
GL_TRIANGLE_STRIP绘制三角形方式很多时候令人疑惑，在这里对其运作机理进行解释。
一般情况下有三种绘制一系列三角形的方式，分别是GL_TRIANGLES、GL_TRIANGLE_STRIP和GL_TRIANGLE_FAN。
如下图所示：
它的渲染根据顶点数据组成方式不同分为两种方式：
一、它的渲染可以通过glGenBuffers，glBindBuffer，glBufferData个来完成。当需要动态修改顶点数据时，通过调用glBufferSubData来完成。
#include "glew.h"
#include <glfw3.h>
#include "common/loadShader.h"
#include "glm.hpp"
#include "ext.hpp"
int main(void)
{
GLFWwindow* window;
/* Initialize the library */
if (!glfwInit())
return -1;
/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(480, 480, "Hello World", NULL, NULL);
if (!window)
{
glfwTerminate();
return -1;
}
/* Make the window's context current */
glfwMakeContextCurrent(window);
// Needed in core profile
if( glewInit() != GLEW_OK)
{
glfwTerminate();
return -1;
}
float g_vertex_buffer_data[] =
{
-1, 1, 1,
-1, -1, 1,
1, 1, 1,
1, -1, 1
};
float g_uv_buffer_data[] =
{
0, 1,
0, 0,
1, 1,
1, 0
};
float g_color_buffer_data[] =
{
1, 1, 1, 1,
1, 1, 1, 1,
1, 1, 1, 1,
1, 1, 1, 1
};
GLuint Texture = loadBMP_custom("./resource/uvtemplate.bmp");
//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 uvbuffer;
glGenBuffers(1,&uvbuffer);
glBindBuffer(GL_ARRAY_BUFFER,uvbuffer);
glBufferData(GL_ARRAY_BUFFER,sizeof(g_uv_buffer_data),g_uv_buffer_data,GL_STATIC_DRAW);
GLuint colorbuffer;
glGenBuffers(1,&colorbuffer);
glBindBuffer(GL_ARRAY_BUFFER,colorbuffer);
glBufferData(GL_ARRAY_BUFFER,sizeof(g_color_buffer_data),g_color_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(-2.0f, 2.0f, -2.0f, 2.0f, 0.1f, 100.0f);
glm::mat4 View = glm::lookAt(
glm::vec3(0,0,100), // 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)
);
glm::mat4 Model = glm::mat4(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]);
GLuint TextureID = glGetUniformLocation(programID,"myTextureSampler");
while (!glfwWindowShouldClose(window))
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glActiveTexture(GL_TEXTURE5);
glBindTexture(GL_TEXTURE_2D,Texture);
glUniform1i(TextureID, 5);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER,vertexbuffer);
//glBufferSubData(GL_ARRAY_BUFFER,0,sizeof(g_vertex_buffer_data),g_vertex_buffer_data);
glVertexAttribPointer(
0, // attribute 0. No particular reason for 0, but must match the layout in the shader.
3, // size
GL_FLOAT, // type
GL_FALSE, // normalized?
0, // stride
(void*)0 // array buffer offset
);
glEnableVertexAttribArray(1);
glBindBuffer(GL_ARRAY_BUFFER,uvbuffer);
//glBufferSubData(GL_ARRAY_BUFFER,0,sizeof(g_uv_buffer_data),g_uv_buffer_data);
glVertexAttribPointer(
1, // attribute 0. No particular reason for 0, but must match the layout in the shader.
2, // size
GL_FLOAT, // type
GL_FALSE, // normalized?
0, // stride
(void*)0 // array buffer offset
);
glEnableVertexAttribArray(2);
glBindBuffer(GL_ARRAY_BUFFER,colorbuffer);
//glBufferSubData(GL_ARRAY_BUFFER,0,sizeof(g_color_buffer_data),g_color_buffer_data);
glVertexAttribPointer(
2, // attribute 0. No particular reason for 0, but must match the layout in the shader.
4, // size
GL_FLOAT, // type
GL_FALSE, // normalized?
0, // stride
(void*)0 // array buffer offset
);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LESS);
glDrawArrays(GL_TRIANGLE_STRIP,0,4);// Starting from vertex 0; 3 vertices total -> 1 triangle
glDisableVertexAttribArray(0);
glDisableVertexAttribArray(1);
glDisableVertexAttribArray(2);
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
glfwTerminate();
return 0;
}
二、 它的渲染可以通过内存数据指针来完成，当需要动态修改顶点数据时，修改内存数据就可以了。
// glfwTest.cpp : 定义控制台应用程序的入口点。
//
#include "glew.h"
#include <glfw3.h>
#include "common/loadShader.h"
#include "glm.hpp"
#include "ext.hpp"
typedef struct {
float Position[3];
float Colors[4];
float TexCoord[2];
} Vertex;
int main(void)
{
GLFWwindow* window;
/* Initialize the library */
if (!glfwInit())
return -1;
/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(320, 320, "Hello World", NULL, NULL);
if (!window)
{
glfwTerminate();
return -1;
}
/* Make the window's context current */
glfwMakeContextCurrent(window);
// Needed in core profile
if( glewInit() != GLEW_OK)
{
glfwTerminate();
return -1;
}
Vertex Vertices[] = {
{{-1, 1, 1}, {1, 1, 1, 1}, {0, 1}},
{{-1, -1, 1}, {1, 1, 1, 1}, {0, 0}},
{{ 1, 1, 1}, {1, 1, 1, 1}, {1, 1}},
{{ 1, -1, 1}, {1, 1, 1, 1}, {1, 0}}
};
GLuint Texture = loadBMP_custom("./resource/uvtemplate.bmp");
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(-2.0f, 2.0f, -2.0f, 2.0f, 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(0,0,100), // 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)
);
glm::mat4 Model = glm::mat4(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]);
GLuint TextureID = glGetUniformLocation(programID,"myTextureSampler");
while (!glfwWindowShouldClose(window))
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glActiveTexture(GL_TEXTURE5);
glBindTexture(GL_TEXTURE_2D,Texture);
glUniform1i(TextureID, 5);
#define kQuadSize sizeof(Vertex)
long offset = (long)Vertices;
int diff = offsetof( Vertex, Position);
glEnableVertexAttribArray(0);
glVertexAttribPointer(
0, // attribute 0. No particular reason for 0, but must match the layout in the shader.
3, // size
GL_FLOAT, // type
GL_FALSE, // normalized?
kQuadSize, // stride
(void*)(offset + diff) // array buffer offset
);
diff = offsetof( Vertex, TexCoord);
glEnableVertexAttribArray(1);
glVertexAttribPointer(
1, // attribute 0. No particular reason for 0, but must match the layout in the shader.
2, // size
GL_FLOAT, // type
GL_FALSE, // normalized?
kQuadSize, // stride
(void*)(offset + diff) // array buffer offset
);
diff = offsetof( Vertex, Colors);
glEnableVertexAttribArray(2);
glVertexAttribPointer(
2, // attribute 0. No particular reason for 0, but must match the layout in the shader.
4, // size
GL_FLOAT, // type
GL_FALSE, // normalized?
kQuadSize, // stride
(void*)(offset + diff) // array buffer offset
);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LESS);
glDrawArrays(GL_TRIANGLE_STRIP,0,4);// Starting from vertex 0; 3 vertices total -> 1 triangle
glDisableVertexAttribArray(0);
glDisableVertexAttribArray(1);
glDisableVertexAttribArray(2);
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
glfwTerminate();
return 0;
}