glutPostRedisplay() does not update display
- by A D
I am currently drawing a rectangle to the screen and would like to move it by using the arrow keys. However, when I press an arrow key the vertex data changes but the display does refresh to reflect these changes, even though I am calling glutPostRedisplay(). Is there something else that I must do?
My code:
#include <GL/glew.h>
#include <GL/freeglut.h>
#include <GL/freeglut_ext.h>
#include <iostream>
#include "Shaders.h"
using namespace std;
const int NUM_VERTICES = 6;
const GLfloat POS_Y = -0.1;
const GLfloat NEG_Y = -0.01;
struct Vertex {
GLfloat x;
GLfloat y;
Vertex() : x(0), y(0) {}
Vertex(GLfloat givenX, GLfloat givenY) : x(givenX), y(givenY) {}
};
Vertex left_paddle[NUM_VERTICES];
void init() {
glClearColor(1.0f, 1.0f, 1.0f, 0.0f);
left_paddle[0] = Vertex(-0.95f, 0.95f);
left_paddle[1] = Vertex(-0.95f, 0.0f);
left_paddle[2] = Vertex(-0.85f, 0.95f);
left_paddle[3] = Vertex(-0.85f, 0.95f);
left_paddle[4] = Vertex(-0.95f, 0.0f);
left_paddle[5] = Vertex(-0.85f, 0.0f);
GLuint vao;
glGenVertexArrays( 1, &vao );
glBindVertexArray( vao );
GLuint buffer;
glGenBuffers(1, &buffer);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(left_paddle),
NULL, GL_STATIC_DRAW);
GLuint program = init_shaders( "vshader.glsl", "fshader.glsl" );
glUseProgram( program );
GLuint loc = glGetAttribLocation( program, "vPosition" );
glEnableVertexAttribArray( loc );
glVertexAttribPointer( loc, 2, GL_FLOAT, GL_FALSE, 0,
0);
glBindVertexArray(vao);
}
void movePaddle(Vertex* array, GLfloat change) {
for(int i = 0; i < NUM_VERTICES; i++) {
array[i].y = array[i].y + change;
}
glutPostRedisplay();
}
void special( int key, int x, int y ) {
switch ( key ) {
case GLUT_KEY_DOWN:
movePaddle(left_paddle, NEG_Y);
break;
}
}
void display() {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 6);
glutSwapBuffers();
}
int main(int argc, char **argv) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(500,500);
glutCreateWindow("Rectangle");
glewInit();
init();
glutDisplayFunc(display);
glutSpecialFunc(special);
glutMainLoop();
return 0;
}
