I am trying to create a red triangle in C using graphics api opengl 2.1 like below:
it will still compile but my code says that there is a error and is in white shown below:
opengl 2.1 is supported!
error!
my code is:
#include <GL/gl.h>
#include <GL/glew.h>
#include <GL/glu.h>
#include <GLFW/glfw3.h>
#include <iostream>
void error_check() {
GLenum error = glGetError();
if (error != NULL) {
std::cout << "error!" << std::endl;
}
}
static unsigned int CompileShader(unsigned int type,
const std::string& source) {
unsigned int id = glCreateShader(type);
const char* src = source.c_str();
glShaderSource(id, 1, &src, nullptr);
glCompileShader(id);
return id;
}
static unsigned int CreateShader(const std::string& vertexshader,
const std::string& fragmentshader) {
unsigned int program = glCreateProgram();
unsigned int vs = CompileShader(GL_VERTEX_SHADER, vertexshader);
unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentshader);
glAttachShader(program, vs);
glAttachShader(program, fs);
glLinkProgram(program);
return program;
}
int main() {
glfwInit();
GLFWwindow* engine_window =
glfwCreateWindow(600, 600, "Senku-Engine 2", NULL, NULL);
if (engine_window == NULL) {
printf("window not opening!..");
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(engine_window);
glewExperimental = GL_TRUE;
glewInit();
if (GLEW_VERSION_2_1 == GL_TRUE) {
std::cout << "opengl 2.1 is supported!" << std::endl;
}
float vertices[6] = {-0.5f, -0.5f, 0.0f, 0.5f, 0.5f, -0.5f};
unsigned int buffer;
glGenBuffers(1, &buffer);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), vertices, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), nullptr);
std::string vertexShader =
"#version 120 core\n"
"layout(location = 0) in vec4 position;\n"
"void main()\n"
"{\n"
" gl_Position = position;\n"
"}\n";
std::string fragmentShader =
"#version 120 core\n"
"layout(location = 0) out vec4 color;\n"
"void main()\n"
"{\n"
" color = vec4(1.0,0.0,0.0,1.0);\n"
"}\n";
unsigned int shader = CreateShader(vertexShader, fragmentShader);
glUseProgram(shader);
error_check();
glViewport(0, 0, 600, 600);
while (!glfwWindowShouldClose(engine_window)) {
glDrawArrays(GL_TRIANGLES, 0, 3);
glfwSwapBuffers(engine_window);
glfwPollEvents();
}
glfwTerminate();
return 0;
}
it seems my code shows the red color when using just one line of code in shader source code but doesn't work if i use more than one string.
CodePudding user response:
The profile string core might not be supported by a pure GLSL 120 implementation, use
#version 120
in and out are GLSL 130, layout qualifiers are GLSL 330. You need
attribute vec4 position;
In the fragment shader, remove the out
variable and do
gl_FragColor = vec4(1.0,0.0,0.0,1.0);
These are the most obvious problems. If you have further errors, use glGetShaderInfoLog
to query the compilation output which tells you about the problems. See Shader error handling.