hi guys recently 'm learning the basics of opengl..
so understanded them i tried to write my first program. At the beginning i tried with the functions that allow you to create buffers for the drawing call. but the linker tell to me that these function are undeclared. so i tried with the old one ( i think maybe i'm wrong) and it works.
so my code is the following
#include <GL/glut.h>
#include <GL/glext.h>
#include <GL/gl.h>
#include <stdlib.h>
#include <stdio.h>
void reshape(int, int);
void display(void);
void keyboard(unsigned char, int, int);
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(500,500);
glutInitWindowPosition (100, 100);
glutCreateWindow(argv[0]);
glClearColor(0.0,0.0,0.0,0.0);
glShadeModel(GL_FLAT);
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutKeyboardFunc(keyboard);
glutMainLoop();
return 0;
}
void reshape(int w, int h)
{
glViewport(0,0,(GLsizei) w, (GLsizei) h);
}
void display(void)
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
GLuint* i;
glGenBuffers(1,i);
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_TRIANGLES);
glColor3f(1.0f,1.00f,1.0f);
glVertex3f(0.5f, 0.0f, 0.0f);
glVertex3f(-0.5f,0.5f, 0.0f);
glVertex3f( 0.0f,-0.5f, 0.0f);
glEnd();
glBegin(GL_TRIANGLES);
glColor3f(1.0f,1.00f,1.0f);
glVertex3f(-0.5f, 0.0f, 0.0f);
glVertex3f(0.5f,0.5f, 0.0f);
glVertex3f(0.0f,-0.5f, 0.0f);
glEnd();
//glutWireCube(10);
glFlush();
}
void keyboard(unsigned char key, int x, int y)
{
switch(key) {
case 'l':
break;
}
}
the problem born with the glGenBuffers and all the gl* functions.
here there is the gcc's commande used
gcc -o cube main.c -lGL -lGLU -lglut
and this is the error
main.c: In function ‘display’:
main.c:40:3: warning: implicit declaration of function ‘glGenBuffers’ [-Wimplicit-function-declaration]
glGenBuffers(1,i);
sorry for my English and thank to all.
You are missing the following line at the beginning of your code
#define GL_GLEXT_PROTOTYPES
#include <GL/glut.h>
#include <GL/glext.h>
#include <GL/gl.h>
#include <stdlib.h>
#include <stdio.h>
It compiles without any warnings like this on my Ubuntu computer, see glGenBuffers not defined?
Related
I have been trying to create a basic OpenGL program in C to display a triangle. Except all I am getting is a black screen.
main.c
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
//#include <GL/glew.h>
#define GL_SILENCE_DEPRECATION
#include "win.h"
#include "shaders/cshader.h"
#include "glew.h"
#define GLFW_INCLUDE_GLCOREARB
#include "glfw3.h"
#include <OpenGL/gl3.h>
int main(void) {
if( !glfwInit()) {
fprintf( stderr, "Failed to initialize GLFW\n" );
return -1;
}
// create window
GLFWwindow* window = createWindow(1280,720);
glewExperimental=GL_TRUE; // Needed in core profile
if (glewInit() != GLEW_OK) {
fprintf(stderr, "Failed to initialize GLEW\n");
return -1;
}
glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);
GLuint VertexArrayID;
glGenVertexArrays(1, &VertexArrayID);
glBindVertexArray(VertexArrayID);
static const GLfloat g_vertex_buffer_data[] = {
-1.0f, -1.0f, 0.0f,
1.0f, -1.0f, 0.0f,
0.0f, 1.0f, 0.0f,
};
// 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);
Shader shader = ShaderInit();
shader.Load(&shader,"/Users/***/Desktop/coding/gl_test/shaders/tri.vert","/Users/***/Desktop/coding/gl_test/shaders/tri.frag");
glUseProgram(shader.program);
glClearColor(0.0f, 0.0f, 0.4f, 0.0f);
glfwMakeContextCurrent(window);
do{
glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
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
);
// Draw the triangle !
// Starting from vertex 0; 3 vertices total -> 1 triangle
glUseProgram(shader.program);
glDrawArrays(GL_TRIANGLES, 0, 3);
glDisableVertexAttribArray(0);
// Swap buffers
if (glGetError() != GL_NO_ERROR){
printf("Err");
}
glfwSwapBuffers(window);
glfwPollEvents();
} // Check if the ESC key was pressed or the window was closed
while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
glfwWindowShouldClose(window) == 0 );
return 0;
}
win.c
#include <stdio.h>
#include <stdlib.h>
#include "/Users/***/Downloads/glew-2.1.0/include/GL/glew.h"
#include "/opt/homebrew/Cellar/glfw/3.3.8/include/GLFW/glfw3.h"
GLFWwindow* createWindow(int WIDTH, int HEIGHT){
glfwWindowHint(GLFW_SAMPLES, 4); // 4x antialiasing
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4); // We want OpenGL 4.1
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 1);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); // We don't want the old OpenGL
// Open a window and create its OpenGL context
GLFWwindow* window; // (In the accompanying source code, this variable is global for simplicity)
window = glfwCreateWindow( WIDTH, HEIGHT, "graphic", NULL, NULL);
if( window == NULL ){
fprintf(stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible.\n" );
glfwTerminate();
return NULL;
}
glfwMakeContextCurrent(window);// Initialize GLEW
glfwPollEvents();
return window;
}
The shader program is basic and it compiles and links correctly. I have a vertex and fragment shader that should make the triangle red.
Even if it is broken, I should still be getting a colored screen because of glClear and glClearColor.
I have tried changing opengl versions as well as linking different files, but nothing shows up.
Here is my makefile:
LIBS=-L/opt/homebrew/lib -L/Users/***/Downloads/glew-2.1.0/lib -lGL -lglew
INC=-I/Users/***/Downloads/glew-2.1.0/include
main:
gcc main.c win.c shaders/cshader.c `pkg-config --cflags glfw3` $(LIBS) $(INC) -g -Wall -framework Cocoa -framework OpenGL `pkg-config --libs glfw3` -o test
Everything appears to link and compile without errors. What should I do.
(I know OpenGL is deprecated on new MacOS versions, but lots of people say that at least basic functionality still works)
I am new to openGL and have a hard time to understand how to actually parametrize the function gluLookat. I what it does but don't know how to know which parameters I should pass to that function and what consequences it will have.
This is my current code and strangely enough I don't even see the axis I drew... I think it is due to the parameters I pass to the function gluLookAt();
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <GL/glut.h>
void init(void)
{
glClearColor(0.8, 0.8, 0.8, 0.0); /* window color white */
glEnable(GL_DEPTH_TEST);
}
void drawScene(void)
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(3.0,3.0,3.0, 0.0,0.0,0.0, 0.0,1.0,0.0);
//used some random parameters...
gluLookAt(0.0, 0.0, 0.0, 5.0, 5.0, 5.0, 0, 1, 0);
//axis
//x
glColor3f(1.0,0.0,0.0);
glLineWidth(1.0);
glBegin(GL_LINES);
glVertex3d(0.0,0.0,0.0);
glVertex3d(1.0,0.0,0.0);
glEnd();
//y
glColor3f(0.0,1.0,0.0);
glLineWidth(1.0);
glBegin(GL_LINES);
glVertex3d(0.0,0.0,0.0);
glVertex3d(1.0,0.0,0.0);
glEnd();
//z
glColor3f(0.0,0.0,1.0);
glLineWidth(1.0);
glBegin(GL_LINES);
glVertex3d(0.0,0.0,0.0);
glVertex3d(1.0,0.0,0.0);
glEnd();
glFlush();
}
void herschaal(){
glViewport(0,0,500,500);
glMatrixMode(GL_PROJECTION);
glOrtho(-10, 10, 10, -10, 10, -10);
glLoadIdentity();
}
int main( int argc, char * argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH );
glutInitWindowPosition(50, 100);
glutInitWindowSize(500, 500);
glutCreateWindow("mijn test");
glutReshapeFunc(herschaal);
init();
glutDisplayFunc(drawScene);
glutMainLoop();
return 0;
}
#include <stdio.h>
#include <stdlib.h>
#include <GL/glew.h>
#include <GL/glut.h>
void changeSize(int w, int h)
{
if(h == 0)
h = 1;
float ratio = w / h;
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glViewport(0, 0, w, h);
gluPerspective(40,ratio,1.5,20);
glMatrixMode(GL_MODELVIEW);
}
void renderScene(void)
{
glClear(GL_COLOR_BUFFER_BIT );
glLoadIdentity();
glTranslatef(0.0,0.0,-5.0);
glDrawArrays(GL_TRIANGLES,0,3);
glutSwapBuffers();
}
void init()
{
GLfloat verts[] = {
0.0, 1.0,
-1.0, -1.0,
1.0, -1.0
};
GLuint bufferid;
glGenBuffers(1,&bufferid);
glBindBuffer(GL_ARRAY_BUFFER,bufferid);
glBufferData(GL_ARRAY_BUFFER,sizeof(verts),verts,GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0,2,GL_FLOAT,GL_FALSE,0,0);
if(glGetError()==GL_NO_ERROR)
printf("no error");
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode( GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowPosition(100,100);
glutInitWindowSize(500,500);
glutCreateWindow("MM 2004-05");
glewInit();
init();
glutDisplayFunc(renderScene);
glutReshapeFunc(changeSize);
if (GLEW_ARB_vertex_program && GLEW_ARB_fragment_program)
printf("Ready for GLSL\n");
else {
printf("No GLSL support\n");
//exit(1);
}
glutMainLoop();
return 0;
}
When using glGenBuffers my screen turns out black and shows no error. If i draw some other shape without using buffers they are displayed but not with buffer objects.
openGL version:3.0
operating system:ubuntu
IDE:eclipse
When using glGenBuffers you're using the OpenGL-3.0 specification. To draw anything in OpenGL-3.0+ you need to use shaders, hence why the screen is black; your triangle isn't being shaded.
You are using calls for generic vertex attributes here:
glEnableVertexAttribArray(0);
glVertexAttribPointer(0,2,GL_FLOAT,GL_FALSE,0,0);
Generic vertex attributes can only be used in combination with shaders. As long as you're using the fixed function pipeline, you also have to use fixed function vertex attributes.
The corresponding calls using fixed function attributes are:
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(2, GL_FLOAT, 0, 0);
I tried on eclipse and got the error "Cannot open output file , Permission denied" when trying to use OpenGL. When I used code::blocks - got the same problems as compiling it by myself at the cmd using gcc -o <file_name>.exe <file_name>.c. And all I got was a list full of "undefined reference" to each function appeared in the program taken from OpenGL headers.
That's the small programs - just printing a red square in the middle.
#include <GL\gl.h>
#include <GL\glu.h>
#include <GL\glut.h>
#include <GL\freeglut.h>
#include <GL\glext.h>
#include <GL\freeglut_ext.h>
#include <GL\freeglut_std.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <windows.h>
void display()
{
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
//Draw a red 1x1 square in center
glBegin(GL_QUADS);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex2f(-0.5f, -0.5f); // x, y
glVertex2f( 0.5f, -0.5f);
glVertex2f( 0.5f, 0.5f);
glVertex2f(-0.5f, 0.5f);
glEnd();
glFlush(); //render now
}
int main(int argc, char** argv)
{
glutInit(&argc, argv); // Initialize GLUT
glutCreateWindow("OpenGL Setup Test"); // Create a window with the given title
glutInitWindowSize(320, 320); // Set the window's initial width & height
glutInitWindowPosition(50, 50); // Position the window's initial top-left corner
glutDisplayFunc(display); // Register display callback handler for window re-paint
glutMainLoop(); // Enter the infinitely event-processing loop
return 0;
}
Here is a simple opengl program by me. I'm trying to clear the screen before I draw a triangle. I've called glClear() in my init() function, however, it seemed that it failed to clear the screen.
#include <stdio.h>
#include <stdlib.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>
void myIdleFunc()
{
glBegin(GL_TRIANGLES);
{
glColor3f(1.0f, 1.0f, 1.0f);
glVertex2f(0.0f, 1.0f);
glVertex2f(-1.0f, -1.0f);
glVertex2f(1.0f, -1.0f);
}
glEnd();
glFlush();
usleep(1000000);
}
void init()
{
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glFlush();
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE);
glutCreateWindow("Hello, World!");
init();
glutIdleFunc(myIdleFunc);
glutMainLoop();
return 1;
}
Here is a screen-shot, the text is from the gnome terminal in the back ground.
Where's your display callback? You shouldn't use the idle function for drawing.
All drawing needs to take place in the appropriate callbacks, the GL context might not be active until glutMainLoop starts running, and with no active context, your commands simply get ignored (without a context, there might not even be a place to store errors for retrieval with glGetError).
NOTE: Usually you want to clear the buffer at the beginning of every frame. You might get away with clearing just once with single-buffering, but double-buffering is better and requires you to somehow render the entire area between each swap.
Your problem is, that you do clear the screen in your initialization code. But you need to clear it every frame, so right at the start of your display (or in your case idle) function.
I don't use GLUT but a really simple way to display something like this is:
while( !done ) { /* Loop until done. Do drawing. */
glClear( GL_COLOR_BUFFER_BIT);
glLoadIdentity();
glBegin(GL_TRIANGLES);
{
glColor3f(1.0f, 1.0f, 1.0f);
glVertex2f(0.0f, 1.0f);
glVertex2f(-1.0f, -1.0f);
glVertex2f(1.0f, -1.0f);
}
glEnd();
glFlush();
SwapBuffers( );
etc... event handling....
}
Run this code and probably you will get the solution.
#include<GL/gl.h>
#include<GL/glut.h>
#include<stdio.h>
double x_0 = -100;
double y_0 = -25;
double x_1 = 100;
double y_1 = -25;
double x_2 = 100;
double y_2 = 25;
double x_3 = -100;
double y_3 = 25;
void
init(void)
{
/*initialize the x-y co-ordinate*/
glClearColor(0,0,0,0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(-320, 319,-240, 239);
glClear(GL_COLOR_BUFFER_BIT);
glFlush();
}
void
drawRectangle()
{
glBegin(GL_LINES);
glVertex2d(x_0, y_0);
glVertex2d(x_1, y_1);
glVertex2d(x_1, y_1);
glVertex2d(x_2, y_2);
glVertex2d(x_2, y_2);
glVertex2d(x_3, y_3);
glVertex2d(x_3, y_3);
glVertex2d(x_0, y_0);
glEnd();
glFlush();
}
int
main(int argc, char *argv[])
{
double x_0, y_0, x_1, y_1;
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(640, 480);
glutInitWindowPosition(400, 400);
glutCreateWindow("Clear Screen");
init();
drawRectangle();
/* clear the screen. You can uncomment following three lines to view the effect of clearing */
// glClearColor(0, 0, 0, 0);
// glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// /* don't forget to flush */
// glFlush();
/***/
glutMainLoop();
}
Compile and run -
gcc file.c -lglut -lGLU -lGL
./a.out