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#include <GL/glew.h>
#include <GL/glut.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <math.h>
void init();
void display();
/* With the introduction of Buffer Objects, a somewhat questionable decision
* regarding the reuse of existing API was made. Specifically the reuse of the
* gl...Pointer functions to supply integers through their `data` parameter
* which is a pointer can lead to serious complications, should a compiler
* decide to implement augmented or tagged pointers.
*
* In many OpenGL tutorials, and even the reference documentation one can
* find that an iteger gets cast into a pointer. From the point of view of
* the C language standard and the interpretation of integers cast to pointer
* this practice should be strongly discouraged. The far better method
* is not to cast the offset integer value to a pointer, but to cast the
* gl...Pointer functions to a type signature that defines the `data` parameter
* to be an integer. To keep the size of the `data` parameter consistent
* use the C standard type `uintptr_t` which is guaranted to be large enough
* to hold the integer representation of a pointer.
*
* The same also goes for the glDraw...Elements functions.
*
* Also see http://stackoverflow.com/a/8284829/524368
*/
void (*glfixVertexOffset)(GLint, GLenum, GLsizei, uintptr_t const) = (void*)glVertexPointer;
void (*glfixTexCoordOffset)(GLint, GLenum, GLsizei, uintptr_t const) = (void*)glTexCoordPointer;
void (*glfixDrawElementsOffset)(GLenum, GLsizei, GLenum, uintptr_t const) = (void*)glDrawElements;
/* Those three functions are part of OpenGL-1.1, hence in the OpenGL ABIs of
* all operating systems with OpenGL support and thus available as symbols
* of the interface library, without additional initialization.
*
* Don't use static const initialization for function pointer obtained
* through the OpenGL extension mechanism!
*/
int main(int argc, char *argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode( GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH );
glutCreateWindow("Minimal VBO example");
glutDisplayFunc(display);
glutIdleFunc(glutPostRedisplay);
glewInit();
init();
glutMainLoop();
return 0;
}
GLuint vertexbufId;
GLuint elementbufId;
void init()
{
glGenBuffers(1, &vertexbufId);
glBindBuffer(GL_ARRAY_BUFFER, vertexbufId);
float const cube[5*8]=
{ /* X Y Z U V */
-1, -1, -1, 0, 0,
1, -1, -1, 1, 0,
1, 1, -1, 1, 1,
-1, 1, -1, 0, 1,
-1, -1, 1, -1, 0,
1, -1, 1, 0, 0,
1, 1, 1, 0, 1,
-1, 1, 1, -1, 1,
};
glBufferData(GL_ARRAY_BUFFER, 5*8*sizeof(float), cube, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glGenBuffers(1, &elementbufId);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementbufId);
unsigned int faces[4*6]=
{
0, 1, 2, 3,
1, 5, 6, 2,
5, 4, 7, 6,
4, 0, 3, 7,
3, 2, 6, 7,
4, 5, 1, 0
};
glBufferData(GL_ELEMENT_ARRAY_BUFFER, 4*6*sizeof(float), faces, GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
}
static float a = 0., b = 0., c = 0.;
void display()
{
int const win_width = glutGet(GLUT_WINDOW_WIDTH);
int const win_height = glutGet(GLUT_WINDOW_HEIGHT);
float const win_aspect = (float)win_width / (float) win_height;
glClearColor(0.5, 0.5, 1., 1.);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glViewport(0, 0, win_width, win_height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glFrustum(-win_aspect, win_aspect, -1, 1, 1, 10);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0, 0, -3);
glRotatef(a += 1.00, 1, 0, 0);
glRotatef(b += 0.66, 0, 1, 0);
glRotatef(c += 0.33, 0, 0, 1);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glBindBuffer(GL_ARRAY_BUFFER, vertexbufId);
glfixVertexOffset( 3, GL_FLOAT, 5*sizeof(float), 0);
glfixTexCoordOffset(2, GL_FLOAT, 5*sizeof(float), 3);
/* After the data source of a Vertex Array has been set
* this setting stays persistent regardless of any other
* state changes. So we can unbind the VBO bufferId here
* without loosing the connection. We must not delete
* the VBO though.
*/
glBindBuffer(GL_ARRAY_BUFFER, 0),
glColor4f(0., 0., 0., 1.),
/* Just drawing a wireframe */
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementbufId);
glfixDrawElementsOffset(GL_QUADS, 24, GL_UNSIGNED_INT, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glutSwapBuffers();
}
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