Vfrdtyky

I'm working on OpenGL application, c++ and Qt5

I wrote basic rendering engine, everything is fine when number of vertexes is relatively small, it plots, pans, zooms, etc. Then I increase number of vertex and application crashes with segmentation fault. On my Linux machine it happens when there are 650000-ish vertexes (the number floats a little, may be +/- 50), on windows laptop it is less. Of course, first thought was about memory overflow, but I got 2Gb GPU memory and 1.6Gb free after I create and fill a buffer with the number of point close to the crash level (memory stats taken from NVX extension, so should be reliable enough).
I made a code some time ago in Python, doing same things, and it worked totally well on the same laptop. Do you have any idea what I do wrong now?

Here are some code snippets:

Vertex shader (simplified as much as possible):

#version 330

uniform mat4 projection;

in vec3 position;



out vec4 a_facecolor;

void main()

{

    gl_Position = projection*vec4(position,1);

    gl_PointSize = 5;

    a_facecolor = vec4(1,0,0,1);

}

Fragment:

in vec4 a_facecolor;



void main(void)

{

    gl_FragColor = a_facecolor; 

}

Array initialization:

#define N_POINTS 600000

....

QVector3D data[N_POINTS];

for (long i=0; i < N_POINTS; i++){

    data[i] = QVector3D((qrand()%100-50)/50.0f*2,

                        (qrand()%100-50)/50.0f*2,

                        (qrand()%100-50)/50.0f*1);

}

buffer.create();

buffer.bind();

buffer.allocate(data, sizeof(data)); 

Rendering:

program.bind();

buffer.bind();

program.setUniformValue("projection", projection*transform);

int vertexLocation = program.attributeLocation("position");

program.enableAttributeArray(vertexLocation);

program.setAttributeBuffer(vertexLocation, GL_FLOAT, 0, 3);

glDrawArrays(GL_LINE_STRIP,0,N_POINTS);

glDrawArrays(GL_POINTS,0,N_POINTS);

Based on answer to comment:

data is an array allocated on the stack. If its size becomes larger than the maximal stack size allowed, which is typically much smaller than the total available memory, the program will crash with a stack overflow.

In order to use heap allocation, try:

std::vector<QVector3D> data(N_POINTS);

and then:

buffer.allocate(data.data(), sizeof(QVector3D)*data.size());