glpointsize() 无法缩小点

Question

我正在尝试编写一个简单的opengl程序，该程序使用glPointSize()和可变pointSize周期性地增长和缩小屏幕中心的单个点。打印pointSize的值并使用调试器单步执行代码似乎显示pointSize在每次迭代时正确更新。当pointSize增加时，该点的渲染似乎也是正确的，但是当pointSize减小时，该点仍然以其在屏幕上的最大大小渲染，并且无论pointSize值增长或缩小多少，都会保持这种方式渲染 - 我不知道为什么。

#include <GLglew.h>
#include <GLFWglfw3.h>
#include <iostream>
#define numVAOs 1
GLuint renderingProgram;
GLuint vao[numVAOs];
GLuint createShaderProgram() {
const char *vshaderSource =
"#version 430    n"
"void main(void) n"
"{ gl_Position = vec4(0.0, 0.0, 0.0, 1.0); }";
const char *fshaderSource =
"#version 430    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);
GLuint vfprogram = glCreateProgram();
glShaderSource(vShader, 1, &vshaderSource, NULL);
glShaderSource(fShader, 1, &fshaderSource, NULL);
glCompileShader(vShader);
glCompileShader(fShader);
glAttachShader(vfprogram, vShader);
glAttachShader(vfprogram, fShader);
glLinkProgram(vfprogram);
return vfprogram;
}
void init() {
renderingProgram = createShaderProgram();
glGenVertexArrays(numVAOs, vao);
glBindVertexArray(vao[0]);
}
GLfloat pointSize = 100.0f;
GLfloat increment = 1.0f;
void display() {
glUseProgram(renderingProgram);
if (pointSize > 200 || pointSize < 2) increment *= -1.0f;
pointSize += increment;
glPointSize(pointSize);
glDrawArrays(GL_POINTS, 0, 1);
}
int main(void) {
if (!glfwInit()) exit(EXIT_FAILURE);
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
GLFWwindow* window = glfwCreateWindow(600, 600, "Test", nullptr, nullptr);
glfwMakeContextCurrent(window);
if (glewInit() != GLEW_OK) exit(EXIT_FAILURE);
glfwSwapInterval(1);
init();
while (!glfwWindowShouldClose(window)) {
display();
glfwSwapBuffers(window);
glfwPollEvents();
}
glfwDestroyWindow(window);
glfwTerminate();
exit(EXIT_SUCCESS);
}

Answer 1

您的代码不会清除屏幕glClear.因此，当点增长时，您可以看到它。当它缩小时，它只是被画在更大的点的"内部"，而你没有注意到它。如果你在改变大小时改变点的颜色，你可以抓住这一点。

只需清除帧开头的颜色缓冲区：

void display() {
// default clear color is black, but you can change it:
//glClearColor(1,0,0,1);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(renderingProgram);
...