CODEWITHSUNDEEP
openglopengl-es
user2681780
user2681780

Reputation: 29

Access violate when using glDrawElement

I write a code use glDrawElement to draw a rectangle:

Vertex verticesData[] =
    {
        Vertex( Vector3 (-0.5f, -0.5f, 0.0f) , Vector3 (1.0f, 0.0f, 0.0f) ), //0 
        Vertex( Vector3 (-0.5f, 0.5f, 0.0f ) , Vector3 (0.0f, 1.0f, 0.0f)  ), //1
        Vertex( Vector3 (0.5f, 0.5f, 0.0f  ) , Vector3 (0.0f, 0.0f, 1.0f)  ), //2
        Vertex( Vector3 (-0.5f, -0.5f, 0.0f) , Vector3 (0.5f, 0.5f, 0.5f) ) //3
    };

    GLubyte indices[] = 
    {
        0, 1, 2, //1
        0, 2, 3  //2
    };

    glGenBuffers(1, &vboId);
    glBindBuffer(GL_ARRAY_BUFFER, vboId);
    glBufferData(GL_ARRAY_BUFFER, sizeof(verticesData), verticesData, GL_STATIC_DRAW);

    glGenBuffers(1, &indexBufferId);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBufferId);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

This is in Init() function. And the program make runetime error (access violate) when run to code line:

glDrawElements(GL_TRIANGLES, 18, GL_UNSIGNED_BYTE, NULL);

This statement is in Draw() function. My code is very long so that i cant post all my code here, but if i replace 2 above code blocks by using glDrawArray, there is no error. So I think the problem is in above code. Anyone help me solve this problem,

Upvotes: 0

Views: 104

Answers (1)

genpfault
genpfault

Reputation: 52084

GLubyte indices[] = 
{
    0, 1, 2, //1
    0, 2, 3  //2
};

...

glDrawElements(GL_TRIANGLES, 18, GL_UNSIGNED_BYTE, NULL);
                             ^^

You have 6 indices. If you tell OpenGL you have 18 it'll read right off the end of your indices array.

Pass in 6 instead.

Upvotes: 1

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