OpenGL Orthographic Sketching With GL_LINE_STRIP - opengl

Question

I am having an issue with openGL when drawing my sketched line to the screen in that it seems to be adding an extra point at the origin which is not in the point list:
(0,0) is definitely not in the points that are in the array to be drawn, just cant seem to reason it out. I would guess that maybe my array size is too big or something but I can't see it
Here is my code for populating the array and the draw call
void PointArray::repopulateObjectBuffer()
{
//Rebind Appropriate VAO
glBindVertexArray( vertex_array_object_id );
//Recalculate Array Size
vertexArraySize = points.size()*sizeof(glm::vec2);
//Rebind Appropriate VBO
glBindBuffer( GL_ARRAY_BUFFER, buffer_object_id );
glBufferData( GL_ARRAY_BUFFER, vertexArraySize, NULL, GL_STATIC_DRAW );
glBufferSubData( GL_ARRAY_BUFFER, 0, vertexArraySize, (const GLvoid*)(&points[0]) );
//Set up Vertex Arrays
glEnableVertexAttribArray( 0 ); //SimpleShader attrib at position 0 = "vPosition"
glVertexAttribPointer( (GLuint)0, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0) );
//Unbind
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
}
void PointArray::draw() {
glBindVertexArray(vertex_array_object_id);
glLineWidth(4);
glDrawArrays( GL_LINE_STRIP, 0, vertexArraySize );
glBindVertexArray(0);
}
and here is where I am adding points in the mouse callback
void mouseMovement(int x, int y)
{
mouseDX = x - lastX ;
mouseDY = y - lastY ;
lastX = x;
lastY = y;
if(mouse_drag)
{
cam->RotateByMouse(glm::vec2(mouseDX*mouseSens, mouseDY * mouseSens));
}
if(sketching)
{
sketchLine.addPoint(glm::vec2((float)x,(float)y));
sketchLine.repopulateObjectBuffer();
updatePickray(x,y);
}
}
Finally my simple ortho vertex shader
in vec2 vPosition;
void main(){
const float right = 800.0;
const float bottom = 600.0;
const float left = 0.0;
const float top = 0.0;
const float far = 1.0;
const float near = -1.0;
mat4 orthoMat = mat4(
vec4(2.0 / (right - left), 0, 0, 0),
vec4(0, 2.0 / (top - bottom), 0, 0),
vec4(0, 0, -2.0 / (far - near), 0),
vec4(-(right + left) / (right - left), -(top + bottom) / (top - bottom), -(far + near) / (far - near), 1)
);
gl_Position = orthoMat * vec4(vPosition, 0.0, 1.0);
}

Answer 1

You seem to be using vertexArraySize as the parameter to glDrawArrays, which is not correct. The count of glDrawArrays should be the number of vertices, not the number of bytes of the vertex array.
In your case I guess it would be glDrawArrays( GL_LINE_STRIP, 0, points.size());.