Question

Code below is working fine and draw a colored triangle equal sides:

GLfloat triangle_pos[] =
                 {
            -0.5, -0.25, 0.0,
             0.5, -0.25, 0.0,
             0.0, 0.559016994, 0.0
                 };

void draw_triangle()
{
 glUseProgram(SHADER.program);

 matrix mv;
 multiply_matrix(VIEW_MATRIX/*ident*/, MODEL_MATRIX/*ident*/, mv);
 matrix mvp;
 multiply_matrix(PROJECTION_MATRIX/*ortho*/, mv, mvp);

 glUniformMatrix4fv(SHADER.uniforms[0]/*um_mvp*/, 1, GL_FALSE, mvp);

 glEnableVertexAttribArray(SHADER.atributes[0]/*av_pos*/);
 glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, triangle_pos);

 glDrawArrays(GL_TRIANGLES, 0, 3);

 glDisableVertexAttribArray(SHADER.atributes[0]/*av_pos*/);

 glUseProgram(0);
}

Vertex shader:

attribute vec4 av_pos;
varying vec4 vv_col;
uniform mat4 um_mvp;
void main()
{
 vv_col = um_mvp * av_pos;
 gl_Position = vv_col; 
} 

Fragment shader:

precision lowp float;
varying vec4 vv_col;
void main()
{
 gl_FragColor = vv_col;
}   

Lets change vertex shader to load color values from outside:

attribute vec4 av_pos;
attribute vec4 av_col;
varying vec4 vv_col;
uniform mat4 um_mvp;
void main()
{
 vv_col = av_col
 gl_Position = um_mvp * av_pos; 
}  

And modified code will be:

GLfloat triangle_pos[] =
                 {
            -0.5, -0.25, 0.0,
             0.5, -0.25, 0.0,
             0.0, 0.559016994, 0.0
                 };

GLfloat triangle_col[]=
                 {
    1.0,0.0,1.0,1.0,
    0.0,1.0,1.0,1.0,
    1.0,0.0,0.0,1.0
                 };



void draw_triangle()
{
 glUseProgram(SHADER.program);

 matrix mv;
 multiply_matrix(VIEW_MATRIX, MODEL_MATRIX, mv);
 matrix mvp;
 multiply_matrix(PROJECTION_MATRIX, mv, mvp);

 glUniformMatrix4fv(SHADER.uniforms[0]/*um_mvp*/, 1, GL_FALSE, mvp);

 glEnableVertexAttribArray(SHADER.atributes[0]/*av_pos*/);
 glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, triangle_pos);

 glEnableVertexAttribArray(SHADER.atributes[1]/*av_col*/);
 glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, triangle_col);

 glDrawArrays(GL_TRIANGLES, 0, 3); // just crashing i can't even glGetError() after that line

 glDisableVertexAttribArray(SHADER.atributes[0]);

 glDisableVertexAttribArray(SHADER.atributes[1]);

 glUseProgram(0);
}

Why glDrawArrays crash and how to fix that?

Answer 1

glEnableVertexAttribArray(SHADER.atributes[0]/*av_pos*/);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, triangle_pos);

glEnableVertexAttribArray(SHADER.atributes[1]/*av_col*/);
glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, triangle_col);

glVertexAttribPointer‘s first argument is the attribute to set. It’s the same value as what you give to glEnableVertexAttribArray. So this should be:

glEnableVertexAttribArray(SHADER.atributes[0]/*av_pos*/);
glVertexAttribPointer(SHADER.atributes[0], 3, GL_FLOAT, GL_FALSE, 0, triangle_pos);

glEnableVertexAttribArray(SHADER.atributes[1]/*av_col*/);
glVertexAttribPointer(SHADER.atributes[1], 4, GL_FLOAT, GL_FALSE, 0, triangle_col);