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bananaoomarang

OpenGL
glDrawArrays segfault, beginner confused

3 posts in this topic

Hi,

I'm rather new to OpenGL programming (did Lazy Foo tutorials, know C++/Java basics, have written Tic Tac Toe and modded Minecraft, loads of small game clones).

I've been trying to get some basic classes working, written from scratch, under Linux with SDL (1.2, so I'm assuming this is a 2.1 context, rather than the 3.0 I've been learning via 'OpenGL Game Programming Second Edition'). using Eclipse as my IDE (code::blocks seems too bare bones)

A few notable problems have arisen, I'm assuming they're mostly related. I have made basic/half written Entity and World classes, posted at the bottom, along with the main loop/init.h, which is pretty much everything, aside from classes which aren't in use here yet.

Basically, I was planning on each entity being drawn with a VBO, which would be created at instantiation then bound on drawing, and deleted on destruction. The World class contains a vector of entities which are iterated over and the relevant methods are called.  

The first problem arises with GLee, as I understand I should just be able to include the header and link to library and I'm good to go with extensions. Eclipse doesn't seem to recognise this though, and says functions like glGenBuffers() cannot be resolved. It compiles fine however. GL also needs to linked as well as GLee even if the header is not included? Does GLee not provide everything GL provides? The compiler (presuming g++) complains otherwise. Since functions like glGenBuffers() were compiling just fine, I assumed Eclipse was being stupid and am ignoring the red underlining.

However, GLEE_ARB_vertex_buffer_object is false, whereas GL_ARB_vertex_buffer_object is true (and my card (nVidia geForce 310M) drivers report that it's supported) which is confusing to me. Is this to do with the 2.1 context? What should I use if not SDL to get a 3.0 context, I like all the other things SDL does above GLut...

Am I being stupid? How can GLee report that something's not supported where GL reports that it is?

Also, I had to #define BUFFER_OFFSET by myself, I don't know whether that's supposed to be there by default or not.

Everything seems to be going just fine until:

[code]glDrawArrays(GL_TRIANGLES, 0, 3);[/code]

Where some major crap goes down! It's definitely this part of the code, I've stepped through with gdb. Here's what gdb reports:

[code]
0x000000004007cf7f in ?? ()
(gdb) backtrace
#0  0x000000004007cf7f in ?? ()
#1  0x0000000040000000 in ?? ()
#2  0x00007ffff085ee68 in ?? ()
#3  0x0000000000000003 in ?? ()
#4  0x0000000000000000 in ?? ()
[/code]

I don't really know how to use a backtrace properly.... And stepping through with Eclipse + gdb doesn't provide anything more useful. I'm assuming it's a basic error in my code! Accessing memory that doesn't exist. Presumably I've set up the VBO improperly, but that might be something to do with the 2.1 context/SDL or the GLee/GL problems.


I'm probably being an idiot, in which case, sorry for wasting your time! Any help/pointers with anything here would be appreciated, but I'd mainly like to be able to spawn one of my entities visibly on the screen!

Thank you so much! I really appreciate your time [img]http://public.gamedev.net//public/style_emoticons/default/smile.png[/img]

Entity.h:

[code]
/*
* Entity.h
*
*  Created on: 11 Jan 2012
*      Author: milo
*/

#ifndef ENTITY_H_
#define ENTITY_H_
#include <vector>
#include "Texture.h"
#include "GLee.h"
#include "GL/glu.h"
#include "SDL/SDL.h"

class Entity {
public:
Entity(float x, float y, int width, int height, bool collision);
virtual ~Entity();
void setX(float x);
void setY(float y);
float getX();
float getY();
void pushVertex(GLfloat x, GLfloat y);
virtual void onUpdate();
virtual void onDraw();
virtual void onEvent();
protected:
float x;
float y;
std::vector<GLfloat> vertices;
Texture tex;
bool collision;
GLuint vertexBuffer;
};

#endif /* ENTITY_H_ */
[/code]

Entity.cpp

[code]
/*
* Entity.cpp
*
*  Created on: 11 Jan 2012
*      Author: milo
*/
#include "Entity.h"
#include <iostream>

Entity::Entity(float x, float y, int width, int height, bool collision) {
//pushVertex(0.0f, 0.0f);
//pushVertex(0.0f, (float)height);
//pushVertex((float)width, (float)height);
//pushVertex((float)width, 0.0f);

#define BUFFER_OFFSET(i) ((char *)NULL + (i))

pushVertex(-1.0f, -0.5f);
pushVertex(1.0f, -0.5f);
pushVertex(0.0f, 0.5f);
glGenBuffers(1, &vertexBuffer);
//TODO apply texture
setX(0.0f);
setY(0.0f);
this->collision = collision;
}

Entity::~Entity() {
}

void Entity::setX(float x) {
this->x = x;
}

void Entity::setY(float y) {
this->y = y;
}

float Entity::getX() {
return x;
}

float Entity::getY() {
return y;
}

void Entity::onDraw() {
std::cout << "beggining drawing\n";
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
std::cout << "buffer bound, sending data\n";
glBufferData(GL_ARRAY_BUFFER, sizeof(float) * vertices.size(), &vertices[0], GL_STATIC_DRAW);
std::cout << "data sent, pointing\n";
glVertexPointer(2, GL_FLOAT, 0, BUFFER_OFFSET(0));
std::cout << "Pointed, Enabling state\n";
glEnableClientState(GL_VERTEX_ARRAY);
std::cout << "Enabled state, drawing\n";
glDrawArrays(GL_TRIANGLES, 0, 3);
glDisableClientState(GL_VERTEX_ARRAY);
std::cout << "finished drawing\n";
}

void Entity::onUpdate() {
}

void Entity::onEvent() {
}

void Entity::pushVertex(GLfloat x, GLfloat y) {
vertices.push_back(x);
vertices.push_back(y);
}
[/code]

World.h:

[code]

/*
* World.h
*
*  Created on: 14 Jan 2012
*      Author: milo
*/

#ifndef WORLD_H_
#define WORLD_H_
#include <vector>
#include "Entity.h"

class World {
public:
World();
virtual ~World();
void handleEvents();
void update();
void draw();
void pushEntity(Entity *entity);
private:
std::vector<Entity> entities;
std::vector<Entity>::iterator enterator;
};

#endif /* WORLD_H_ */
[/code]

World.cpp:

[code]

/*
* World.cpp
*
*  Created on: 14 Jan 2012
*      Author: milo
*/

#include "World.h"

World::World() {
}

World::~World() {
// TODO Auto-generated destructor stub
}

void World::update() {
for (enterator = entities.begin(); enterator != entities.end(); ++enterator) {
enterator->onUpdate();
}
}

void World::handleEvents() {
for (enterator = entities.begin(); enterator != entities.end(); ++enterator) {
enterator->onEvent();
}
}

void World::draw() {
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
for (enterator = entities.begin(); enterator != entities.end(); ++enterator) {
enterator->onDraw();
}
}

void World::pushEntity(Entity *entity) {
entities.push_back(*entity);
}
[/code]

And the main file is as follows:

[code]


//============================================================================
// Name        : Crysis.cpp
// Author      : Milo Mordaunt
// Version     :
// Copyright   : Please copy. Please steal.
// Description : The single most powerful piece of software ever to exist on
//  this planet we call Earth.
//============================================================================
#include "init.h"
#include <vector>
#include "World.h"

int main() {
bool quit = false;
if (GLEE_ARB_vertex_buffer_object) {
cout << "supported!\n";
}
//Texture* texture = new Texture();
World* world = new World();
Entity* entity = new Entity(100.0f, 100.0f, 20, 20, true);

world->pushEntity(entity);

if (init() == false) {
printf("Unable to initialize: %s\n", SDL_GetError());
}

while(!quit) {
while (SDL_PollEvent(&event)) {
//yup
world->handleEvents();
if (event.type == SDL_QUIT) {
quit = true;
}
}

world->draw();
world->update();

SDL_GL_SwapBuffers();
}

    SDL_Quit();

return 0;
}

[/code]

init.h sets up some variables/init functions:

[code]

/*
* init.h
*
*  Created on: 11 Jan 2012
*      Author: milo
*/

#ifndef INIT_H_
#define INIT_H_

#include <iostream>
#include "GLee.h"
#include "GL/glu.h"
#include "SDL/SDL.h"

using namespace std;

const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;

const int FRAME_RATE = 60;

SDL_Event event;

bool init_GL()
{
glClearColor( 0.0f, 0.0f, 0.0f, 0.0f );

    glViewport( 0, 0, 640, 480 );

    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();

    glOrtho( 0, SCREEN_WIDTH, SCREEN_HEIGHT, 0, -1, 1 );

    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();

    //If there was any errors
    if( glGetError() != GL_NO_ERROR )
    {
        return false;
    }

    //If everything initialized
    return true;
}

bool init()
{
SDL_Surface *screen;

// Slightly different SDL initialization
if ( SDL_Init(SDL_INIT_EVERYTHING) != 0 ) {
        printf("Unable to initialize SDL: %s\n", SDL_GetError());
        return 1;
}

screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_OPENGL ); // *changed*
    if ( !screen ) {
     printf("Unable to set video mode: %s\n", SDL_GetError());
     return 1;
    }

    //Initialize OpenGL
    if( init_GL() == false )
    {
        return false;
    }

    //Set caption
    SDL_WM_SetCaption( "OpenGL Test", NULL );



    //If everything initialized fine
    return true;
}

#endif /* INIT_H_ */

[/code]
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[quote]Am I being stupid? How can GLee report that something's not supported where GL reports that it is?[/quote]
I think that GLEE is over. Try GLEW or GL3W
http://www.opengl.org/wiki/OpenGL_Loading_Library
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The GLEE-names, if I remember correct, are queried at runtime and set once the [i]driver[/i] has reported something as supported. This also require you to initialize OpenGL [i]before [/i]GLEE, so the environment is set up for GLEE to work in the first place. These names reflects that your driver is actually capable of.

The GL-names are, however, compile time constants that reports whether the [i]library[/i] provides the necessary interface. It has nothing to do with it being supported by the driver or not, only that the necessary interface is available to you when compiling.
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Thanks for the quick replies!

I switched to Glew, including GL/glew.h and linking GLEW instead of glee, then putting this in the init_gl() function (called after a context is obtained through SDL)

Also removed glu.h/lib, because apparently glew includes that also.

[code]

glewExperimental = true;
GLenum err = glewInit();
if (GLEW_OK != err) {
std::cout << "glewinit FAILED";
}
fprintf(stdout, "Status: Using GLEW %s\n", glewGetString(GLEW_VERSION));
[/code]

And it reports that glew is indeed, OK.

GLEW_ARB_vertex_buffer_object == true also!

Eclipse still fails to realise that glGenBuffers et al can be used, as well as GLEW_* bool values, underlining them in red, but it compiles.....

And fails to run, segfaulting at the use of:

[code]glGenBuffers(1, &vertexBuffer);[/code]

here's a (decidedly more useful this time) backtrace:

[code]

(gdb) backtrace
#0 0x0000000000000000 in ?? ()
#1 0x0000000000401a11 in Entity::Entity (this=0x607750, x=100, y=100, width=20, height=20, collision=true) at ../src/Entity.cpp:20
#2 0x000000000040183a in main () at ../src/Crysis.cpp:20
[/code]

Am I using glew wrong still?

EDIT: Damn!! I've been stupid. stupid stupid stupid!!! I queried the GL_VERSION with glGetString before glGenBuffers, just to quickly see what context I had, and the program returned.... NULL. What the.... I thought... But I was.... Drawing to the.... Wait.... IT CAN'T BE!!

I instantiated the Entity BEFORE I ran the init function, at the top of main, generating and filling a buffer before I had a context!! So I guess the buffer generated didn't really exist, so when I bound nothing nothing was reported, but when I tried to draw it OpenGL (understandably) freaked out.

It's not crashing and it's reporting 'finished drawing' so I'll assume it's been drawn (hasn't been translated of colored, or gluLooked at so I'll assume it's being 'shown' somewhere, I'll report back if it's not!)

Thanks so much, I really appreciated the help! Any other advice about anything I'm doing really badly here, please say!

EDIT2: Wasn't drawing, you have to bind the buffer before you send the data, then again before you draw, I was binding just pre-draw! Awesome.
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    • By Tchom
      Hey devs!
       
      I've been working on a OpenGL ES 2.0 android engine and I have begun implementing some simple (point) lighting. I had something fairly simple working, so I tried to get fancy and added color-tinting light. And it works great... with only one or two lights. Any more than that, the application drops about 15 frames per light added (my ideal is at least 4 or 5). I know implementing lighting is expensive, I just didn't think it was that expensive. I'm fairly new to the world of OpenGL and GLSL, so there is a good chance I've written some crappy shader code. If anyone had any feedback or tips on how I can optimize this code, please let me know.
       
      Vertex Shader
      uniform mat4 u_MVPMatrix; uniform mat4 u_MVMatrix; attribute vec4 a_Position; attribute vec3 a_Normal; attribute vec2 a_TexCoordinate; varying vec3 v_Position; varying vec3 v_Normal; varying vec2 v_TexCoordinate; void main() { v_Position = vec3(u_MVMatrix * a_Position); v_TexCoordinate = a_TexCoordinate; v_Normal = vec3(u_MVMatrix * vec4(a_Normal, 0.0)); gl_Position = u_MVPMatrix * a_Position; } Fragment Shader
      precision mediump float; uniform vec4 u_LightPos["+numLights+"]; uniform vec4 u_LightColours["+numLights+"]; uniform float u_LightPower["+numLights+"]; uniform sampler2D u_Texture; varying vec3 v_Position; varying vec3 v_Normal; varying vec2 v_TexCoordinate; void main() { gl_FragColor = (texture2D(u_Texture, v_TexCoordinate)); float diffuse = 0.0; vec4 colourSum = vec4(1.0); for (int i = 0; i < "+numLights+"; i++) { vec3 toPointLight = vec3(u_LightPos[i]); float distance = length(toPointLight - v_Position); vec3 lightVector = normalize(toPointLight - v_Position); float diffuseDiff = 0.0; // The diffuse difference contributed from current light diffuseDiff = max(dot(v_Normal, lightVector), 0.0); diffuseDiff = diffuseDiff * (1.0 / (1.0 + ((1.0-u_LightPower[i])* distance * distance))); //Determine attenuatio diffuse += diffuseDiff; gl_FragColor.rgb *= vec3(1.0) / ((vec3(1.0) + ((vec3(1.0) - vec3(u_LightColours[i]))*diffuseDiff))); //The expensive part } diffuse += 0.1; //Add ambient light gl_FragColor.rgb *= diffuse; } Am I making any rookie mistakes? Or am I just being unrealistic about what I can do? Thanks in advance
    • By yahiko00
      Hi,
      Not sure to post at the right place, if not, please forgive me...
      For a game project I am working on, I would like to implement a 2D starfield as a background.
      I do not want to deal with static tiles, since I plan to slowly animate the starfield. So, I am trying to figure out how to generate a random starfield for the entire map.
      I feel that using a uniform distribution for the stars will not do the trick. Instead I would like something similar to the screenshot below, taken from the game Star Wars: Empire At War (all credits to Lucasfilm, Disney, and so on...).

      Is there someone who could have an idea of a distribution which could result in such a starfield?
      Any insight would be appreciated
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