我在我的大学学习计算机图形学课程。我需要在现代OpenGL(3.3+)中实现基本的线条绘制算法,以在屏幕上绘制基元。这是我想要实现的Bresenham线绘制算法的功能 -
void bresenham(GLint xStart, GLint yStart, GLint xEnd, GLint yEnd) {
if (!(xStart < xEnd)) {
swap(xStart, xEnd);
swap(yStart, yEnd);
}
GLint dx = xEnd - xStart;
GLint dy = yEnd - yStart;
GLint p = 2 * dy - dx;
GLint x = xStart;
GLint y = yStart;
setPixel(x,y);
while (x < xEnd) {
x += 1;
if (p < 0)
p += (2 * dy);
else {
p += (2 * (dy - dx));
y += 1;
setPixel(x,y);
}
}
}
我对如何实现setPixel()
功能一无所知。我在这里和其他地方找到的大多数答案都使用较旧的OpenGL函数 -
void setPixel(int x, int y)
{
glColor3f(0.0, 0.0, 0.0); //Set pixel to black
glBegin(GL_POINTS);
glVertex2i(x, y); //Set pixel coordinates
glEnd();
glFlush(); //Render pixel
}
在OpenGl 3.3+中执行此操作的等效方法是什么?
假设我可以添加&#34;像素&#34;到std::vector
数组,如何初始化顶点缓冲区数组来存储这些数据?
我在尝试使用GL_POINTS
绘制点时遇到的另一个问题是,由于在转换为规范化设备坐标时剪切,超出范围[-1,1]的任何一个方向上的点都不显示在窗口。
例如,只有前三个点显示在窗口屏幕上。请参阅initialize()
功能 -
#include <stdio.h>
#include <stdlib.h>
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <cstdlib>
#include <vector>
#include <iostream>
#include <fstream>
// Read a shader source from a file
// store the shader source in a std::vector<char>
void read_shader_src(const char* fname, std::vector<char> &buffer);
// Compile a shader
GLuint load_and_compile_shader(const char *fname, GLenum shaderType);
// Create a program from two shaders
GLuint create_program(const char *path_vert_shader, const char *path_frag_shader);
// Render scene
void display(GLuint &vao, GLFWwindow* window);
// Initialize the data to be rendered
void initialize(GLuint &vao);
//GLFW Callbacks
static void error_callback(int error, const char* description) {
fprintf(stderr, "Error: %s\n", description);
}
static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods) {
if(key == GLFW_KEY_ESCAPE && action == GLFW_PRESS) {
glfwSetWindowShouldClose(window, GL_TRUE);
}
}
int main() {
glfwSetErrorCallback(error_callback);
//Initialize GLFW
if (!glfwInit()) {
fprintf(stderr, "Failed to initialize GLFW.\n");
return -1;
}
//Set GLFW window settings and create window
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
GLFWwindow* window = glfwCreateWindow(500, 500, "My window", NULL, NULL);
if(!window) {
fprintf(stderr, "Window or context creation failed.\n");
return -1;
}
glfwSetKeyCallback(window, key_callback);
glfwMakeContextCurrent(window);
//Initialize GLEW
glewExperimental = GL_TRUE;
if(glewInit() != GLEW_OK) {
fprintf(stderr, "Failed to initialize glew");
glfwTerminate();
return -1;
}
//Create a vertex array object
GLuint vao;
//Initialize the data to be rendered
initialize(vao);
while (!glfwWindowShouldClose(window)) {
display(vao, window);
glfwPollEvents();
}
glfwTerminate();
return 0;
}
//Render scene
void display(GLuint &vao, GLFWwindow* window) {
//Red background
glClearColor(1.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
glBindVertexArray(vao);
glDrawArrays(GL_POINTS, 0, 12);
// Swap front and back buffers
glfwSwapBuffers(window);
}
void initialize(GLuint &vao) {
glEnable(GL_PROGRAM_POINT_SIZE);
// Use a Vertex Array Object
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
//Store verex positions in an array
GLfloat vertices[24] = {
0.0, 0.0, // Only these
0.5, 0.5, //three points show up
1.0, 1.0, //on the window screen
4.0, 4.0,
5.0, 5.0,
6.0, 6.0,
7.0, 7.0,
8.0, 8.0,
9.0, 9.0,
10.0, 10.0,
11.0, 11.0,
12.0, 12.0,
};
//Create a vertex buffer object to store the vertex data
GLuint vbo;
//Generates 1 buffer object name and stores it in vbo
glGenBuffers(1, &vbo);
//Bind the buffer object to the buffer binding target
glBindBuffer(GL_ARRAY_BUFFER, vbo);
//Creates and initializes the buffer object's data store(with data from vertices)
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
GLuint shaderProgram = create_program("/Users/.../vert.shader", "/Users/.../frag.shader"); //path to shader files
// Get the location of the attributes that enters in the vertex shader
GLint posAttrib = glGetAttribLocation(shaderProgram, "position");
// Specify how the data for position can be accessed
glVertexAttribPointer(posAttrib, 2, GL_FLOAT, GL_FALSE, 0, 0);
//Enable the attribute
glEnableVertexAttribArray(posAttrib);
}
// Read a shader source from a file
// store the shader source in a std::vector<char>
void read_shader_src(const char *fname, std::vector<char> &buffer) {
std::ifstream in;
in.open(fname, std::ios::binary);
if(in.is_open()) {
// Get the number of bytes stored in this file
in.seekg(0, std::ios::end);
size_t length = (size_t)in.tellg();
// Go to start of the file
in.seekg(0, std::ios::beg);
// Read the content of the file in a buffer
buffer.resize(length + 1);
in.read(&buffer[0], length);
in.close();
// Add a valid C - string end
buffer[length] = '\0';
}
else {
std::cerr << "Unable to open " << fname << " I'm out!" << std::endl;
exit(-1);
}
}
//Compile a shader
GLuint load_and_compile_shader(const char* fname, GLenum shaderType) {
//Load a shader from an external file
std::vector<char> buffer;
read_shader_src(fname, buffer);
const char *src = &buffer[0];
//Create and compile the shader
GLuint shader = glCreateShader(shaderType);
glShaderSource(shader, 1, &src, NULL);
glCompileShader(shader);
GLint shader_compiled;
glGetShaderiv(shader, GL_COMPILE_STATUS, &shader_compiled);
if(!shader_compiled) {
GLchar message[1024];
glGetShaderInfoLog(shader, 1024, NULL, message);
std::cerr << "Shader compilation failed.";
std::cerr << "Log: " << &message << std::endl;
glfwTerminate();
exit(-1);
}
return shader;
}
// Create a program from two shaders
GLuint create_program(const char *path_vert_shader, const char *path_frag_shader) {
// Load and compile the vertex and fragment shaders
GLuint vertexShader = load_and_compile_shader(path_vert_shader, GL_VERTEX_SHADER);
GLuint fragmentShader = load_and_compile_shader(path_frag_shader, GL_FRAGMENT_SHADER);
// Attach the above shader to a program
GLuint shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
// Flag the shaders for deletion
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
// Link and use the program
glLinkProgram(shaderProgram);
glUseProgram(shaderProgram);
return shaderProgram;
}
我做了哪些修改,所以我可以绘制其余的点?
顶点着色器 -
#version 150 core
in vec4 position;
void main() {
gl_Position = position;
gl_PointSize = 10.0;
}
片段着色器 -
#version 150 core
out vec4 out_color;
void main() {
out_color = vec4(1.0, 1.0, 1.0, 1.0);
}
答案 0 :(得分:3)
从评论中可以看出,您正在尝试使用OpenGL代替类所需的非常古老的图形库。由于计算机图形已经发生了很大变化,以至于你在现代OpenGL中尝试做的事情是不合理的,你应该尝试为当前的作业和后来的作业做这个:
免责声明:这不是在现代OpenGL中划线的合理方法
setPixel
函数一些粗糙的伪代码:
GLuint tex;
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_2D, tex);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, w, h, 0, GL_RGB, GL_FLOAT, pixels);
glBindTexture(GL_TEXTURE_2D, 0);
然后你会创建一个四边形(实际上只是两个三角形),将这个纹理绘制到屏幕上。在open.gl指南之后应该运行良好,因为他们已经为它们的纹理做了这个。从他们提供的代码中拉出来(这有点多余,所有正确并遵循规范):
GLfloat vertices[] = {
// Position Color Texcoords
-0.5f, 0.5f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, // Top-left
0.5f, 0.5f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f, // Top-right
0.5f, -0.5f, 0.0f, 0.0f, 1.0f, 1.0f, 1.0f, // Bottom-right
-0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f // Bottom-left
};
GLuint elements[] = {
0, 1, 2,
2, 3, 0
};
// Set up buffer objects, create shaders, initialize GL, etc.
//drawing
//bind buffers, enable attrib arrays, etc
glBindTexture(GL_TEXTURE_2D, tex);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);