本文主要是介绍OpenGL——着色器画一个点,希望对大家解决编程问题提供一定的参考价值,需要的开发者们随着小编来一起学习吧!
一、 绘制
在窗口中间画一个像素点:
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>using namespace std;#define numVAOs 1GLuint renderingProgram;
GLuint vao[numVAOs];GLuint
createShaderProgram ()
{const char *vshaderSource = "#version 460 \n""void main(void) \n""{ gl_Position = vec4(0.0, 0.0, 0.0, 1.0); }";const char *fshaderSource = "#version 460 \n""out vec4 color; \n""void main(void) \n""{ color = vec4(0.0, 0.0, 1.0, 1.0); }";GLuint vShader = glCreateShader (GL_VERTEX_SHADER);GLuint fShader = glCreateShader (GL_FRAGMENT_SHADER);glShaderSource (vShader, 1, &vshaderSource, NULL);glShaderSource (fShader, 1, &fshaderSource, NULL);glCompileShader (vShader);glCompileShader (fShader);GLuint vfProgram = glCreateProgram();glAttachShader (vfProgram, vShader);glAttachShader (vfProgram, fShader);glLinkProgram (vfProgram);return vfProgram;
}void
display (GLFWwindow *window, double currTime)
{glUseProgram (renderingProgram);glDrawArrays (GL_POINTS, 0, 1);
}void
init (GLFWwindow *window)
{renderingProgram = createShaderProgram();glGenVertexArrays (numVAOs, vao);glBindVertexArray (vao[0]);
}int
main (int argc, char *argv[])
{if (!glfwInit()) {return -1;}glfwWindowHint (GLFW_CONTEXT_VERSION_MAJOR, 4);glfwWindowHint (GLFW_CONTEXT_VERSION_MINOR, 6);GLFWwindow *window = glfwCreateWindow (600, 600, "Chapter2 - program1", nullptr, nullptr);glfwMakeContextCurrent (window);int errorCode = glewInit();if (errorCode != GLEW_OK) {cerr << "Error: " << glewGetErrorString (errorCode) << endl;return -1;}glfwSwapInterval (1);init (window);while (!glfwWindowShouldClose (window)) {display (window, glfwGetTime());glfwSwapBuffers (window);glfwPollEvents();}glfwDestroyWindow (window);glfwTerminate();return 0;
}
点太小了很难看见,可以把它调大点:
void
display(GLFWindow *window, double currTime)
{glUseProgram(renderingProgram);glPointSize(30);glDrawArrays(GL_POINTS, 0, 1);
}
现在,栅格化阶段从顶点着色器收到顶点时,会设置像素的颜色,组成一个尺寸为30像素的点。
二、预定义变量说明
1. gl_Position
内置变量gl_Position
用来设置顶点在3D空间中的坐标位置,并将其发送到下一个管线阶段。
GLSL数据类型vec4用来存储四元组,适合用来存储坐标,四元组的前3个值分别表示x、y、z坐标,第4个值在这里设为1.0(暂时不用了解)。
本例中,顶点坐标被硬编码为原点。
2. gl_FragCord
还可以用预定义变量gl_FragCord
来控制颜色,
修改着色器代码:
fshaderSource = R"(
#version 460
out vec4 color;
void main(void)
{if(gl_FragCoord.x < 295)color = vec4(1.0, 0.0, 0.0, 1.0);elsecolor = vec4(0.0, 0.0, 1.0, 1.0);
}
)";
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