problems generating texture - opengl

Question

Update 2 works, it was a wrong allert
Update 2 (using vbo vertex- and fragment-shaders) but it still don't works
#include "GL/glxew.h"
#include "GL/glext.h"
#include "GL/glu.h"
#include "GL/freeglut.h"
#include <iostream>
GLint attribute;
GLuint program;
void gen_texture(GLuint &texture, int width, int height)
{
GLuint fb;
glGenFramebuffers(1, &fb);
glGenTextures(1, &texture);
glBindFramebuffer(GL_FRAMEBUFFER, fb);
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D,
0,
GL_RGBA,
width, height,
0,
GL_RGBA,
GL_UNSIGNED_BYTE,
0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);
glBindTexture(GL_TEXTURE_2D, 0);
glEnable(GL_TEXTURE_2D);
glBindFramebuffer(GL_FRAMEBUFFER, fb);
glClearColor(1,1,1,0);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(program);
glEnableVertexAttribArray(attribute);
GLfloat vertex_data[]
{
1.0f, 0.0f,
0.0f, 0.0f,
0.0f, 1.0f,
1.0f, 0.0f,
0.0f, 1.0f,
1.0f, 1.0f
};
glVertexAttribPointer(
attribute,
2,
GL_FLOAT,
GL_FALSE,
0,
vertex_data
);
glDrawArrays(GL_TRIANGLES, 0, 6);
glDisableVertexAttribArray(attribute);
}
void init_layout()
{
GLint compile_ok = GL_FALSE, link_ok = GL_FALSE;
GLuint vs, fs;
vs = glCreateShader(GL_VERTEX_SHADER);
const char *vs_source =
"#version 120\n" // OpenGL 2.1
"attribute vec2 coord2d; "
"void main(void) { "
" gl_Position = vec4(coord2d, 0.0, 1.0); "
"}";
glShaderSource(vs, 1, &vs_source, 0);
glCompileShader(vs);
glGetShaderiv(vs, GL_COMPILE_STATUS, &compile_ok);
if (0 == compile_ok)
{
std::cerr << "[texture_layout/init_layout] fehler im vertex shader\n";
exit(1);
}
fs = glCreateShader(GL_FRAGMENT_SHADER);
const char *fs_source =
"#version 120\n" // OpenGL 2.1
"void main(void) { "
" gl_FragColor[0] = 0.8f; "
" gl_FragColor[1] = 0.5f;"
" gl_FragColor[2] = 0.0f; "
"}";
glShaderSource(fs, 1, &fs_source, 0);
glCompileShader(fs);
glGetShaderiv(fs, GL_COMPILE_STATUS, &compile_ok);
if (0 == compile_ok)
{
std::cerr << "[texture_layout/init_layout] fehler im fragment shader\n";
exit(1);
}
program = glCreateProgram();
glAttachShader(program, vs);
glAttachShader(program, fs);
glLinkProgram(program);
glGetProgramiv(program, GL_LINK_STATUS, &link_ok);
if (!link_ok)
{
std::cerr << "[texture_layout/init_layout] fehler in glLinkProgram\n";
exit(1);
}
const char* attribute_name = "coord2d";
attribute = glGetAttribLocation(program, attribute_name);
if (attribute == -1) {
std::cerr << "Could not bind attribute " << attribute_name << "\n";
exit(1);
}
}
int main(int argc, char **argv)
{
glutInit (&argc, argv);
glutInitContextProfile(GLUT_CORE_PROFILE);
glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowSize (500, 500);
glutCreateWindow ("");
glewExperimental=GL_TRUE;
GLenum err=glewInit();
if(err!=0)
{
std::cerr << glewGetErrorString(err) << std::endl;
exit(1);
}
GLenum error;
GLuint texture;
while ( ( error = glGetError() ) != GL_NO_ERROR)
{
std::cerr << std::hex << error << "\n";
}
init_layout();
gen_texture(texture, 200, 200);
GLvoid *tex_data = new GLubyte[4*200*200];
glBindTexture(GL_TEXTURE_2D, texture);
glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA, GL_UNSIGNED_BYTE, tex_data);
return 0;
}
Update 1 (using vbo instead of glBegin)
now my code should draw a red triangle using vbo, but it doesn't
void gen_texture(GLuint &color, int width, int height)
{
GLuint fb;
glGenFramebuffers(1, &fb);
glGenTextures(1, &color);
glBindFramebuffer(GL_FRAMEBUFFER, fb);
glBindTexture(GL_TEXTURE_2D, color);
glTexImage2D(GL_TEXTURE_2D,
0,
GL_RGBA,
width, height,
0,
GL_RGBA,
GL_UNSIGNED_BYTE,
0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, color, 0);
glBindTexture(GL_TEXTURE_2D, 0);
glEnable(GL_TEXTURE_2D);
glBindFramebuffer(GL_FRAMEBUFFER, fb);
glMatrixMode(GL_PROJECTION);
glLoadIdentity;
glViewport(0,0,width,height);
glOrtho(0,width,0,height,0,128);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glClearColor(0, 0, 0, 0);
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glDisable(GL_DEPTH_TEST);
//glDisable(GL_CULL_FACE);
glColor3f(1.f, .0f, .0f);
GLfloat vertices[6] =
{
0, 0,
0, (GLfloat)height,
(GLfloat)width, (GLfloat)height,
};
unsigned short indices[] = {0, 1, 2};
GLuint vbo;
glGenBuffersARB(1, &vbo);
glBindBufferARB(GL_ARRAY_BUFFER_ARB, vbo);
glBufferDataARB(GL_ARRAY_BUFFER_ARB, 6*sizeof(GLfloat), vertices, GL_STATIC_DRAW_ARB);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, 0);
glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_SHORT, vertices);
}
Original 2:
I have a function that should draw a red square into a texture with the glBegin directive. But the only thing I got to work is
glClearColor(0, 0, 0, 0);
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
I've tested it with multiple colors. But that part do not work:
glMatrixMode(GL_PROJECTION);
glLoadIdentity;
glViewport(0,0,width,height);
glOrtho(0,width,0,height,0,128);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glDisable(GL_DEPTH_TEST);
glColor3f(1.f, .0f, .0f);
glBegin(GL_QUADS);
glVertex2f(0, 0);
glVertex2f(0, height);
glVertex2f(width, height);
glVertex2f(width, 0);
glEnd();
Here is the full function:
void gen_texture(GLuint &color, int width, int height)
{
GLuint fb;
glGenFramebuffers(1, &fb);
glGenTextures(1, &color);
glBindFramebuffer(GL_FRAMEBUFFER, fb);
glBindTexture(GL_TEXTURE_2D, color);
glTexImage2D(GL_TEXTURE_2D,
0,
GL_RGBA,
width, height,
0,
GL_RGBA,
GL_UNSIGNED_BYTE,
0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, color, 0);
glBindTexture(GL_TEXTURE_2D, 0);
glEnable(GL_TEXTURE_2D);
glBindFramebuffer(GL_FRAMEBUFFER, fb);
glMatrixMode(GL_PROJECTION);
glLoadIdentity;
glViewport(0,0,width,height);
glOrtho(0,width,0,height,0,128);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glClearColor(0, 0, 0, 0);
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glDisable(GL_DEPTH_TEST);
//glDisable(GL_CULL_FACE);
glColor3f(1.f, .0f, .0f);
glBegin(GL_QUADS);
glVertex2f(0, 0);
glVertex2f(0, height);
glVertex2f(width, height);
glVertex2f(width, 0);
glEnd();
}
Original Post:
I have a function that should draw a red square into a texture, but when I call the function for generating the texture and then I want to check the generated texture data, with the glGetTexImage function, I get a null-pointer.
#include "GL/glxew.h"
#include "GL/glext.h"
#include "GL/glu.h"
#include "GL/freeglut.h"
#include <iostream>
GLuint texture;
GLvoid *tex_data;
void gen_texture(GLuint &color, int width, int height)
{
GLuint fb;
glGenFramebuffers(1, &fb);
glGenTextures(1, &color);
glBindFramebuffer(GL_FRAMEBUFFER, fb);
glTexImage2D(GL_TEXTURE_2D,
0,
GL_RGBA,
width, height,
0,
GL_RGBA,
GL_UNSIGNED_BYTE,
0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, color, 0);
glBindTexture(GL_TEXTURE_2D, 0);
glEnable(GL_TEXTURE_2D);
glBindFramebuffer(GL_FRAMEBUFFER, fb);
glViewport(0, 0, width, height);
glClearColor(1,1,1,0);
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
glOrtho (0, width, height, 0, 0, 1);
glMatrixMode (GL_MODELVIEW);
glDisable(GL_DEPTH_TEST);
glDisable(GL_CULL_FACE);
glColor4f(1.f, .0f, .0f, .5f);
glBegin(GL_QUADS);
glVertex2f(0, 0);
glVertex2f(0, height);
glVertex2f(width, height);
glVertex2f(width, 0);
glEnd();
}
int main(int argc, char **argv)
{
glutInit (&argc, argv);
glutInitContextVersion(3, 2);
glutInitContextProfile(GLUT_CORE_PROFILE);
glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowSize (500, 500);
glutCreateWindow ("");
glewExperimental=GL_TRUE;
GLenum err=glewInit();
if(err!=0)
{
std::cerr << glewGetErrorString(err) << std::endl;
exit(1);
}
GLenum error;
while ( ( error = glGetError() ) != GL_NO_ERROR)
{
std::cerr << std::hex << error << "\n";
}
gen_texture(texture, 200, 200);
glBindTexture(GL_TEXTURE_2D, texture);
glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA, GL_UNSIGNED_BYTE, tex_data);
if (tex_data == 0)
std::cerr << "Captain, eine Null an Board!\n";
return 0;
}
the tex_data is now a null-pointer
what am I doing wrong???

Answer 1

glutInitContextVersion(3, 2);
glutInitContextProfile(GLUT_CORE_PROFILE);
^^^^^^^^^^^^^^^^^ ok...
....
glBegin(GL_QUADS);
^^^^^^^^ wat
glBegin() and friends aren't valid calls in a Core context.
You'll have to get spun up on shaders and VBOs if you insist on Core.