glDrawRangeElements of GL_TRIANGLE_STRIP not working properly (using glMapBuffer) - c++

Question

I am trying to render points from a VBO and a Element Buffer Object with glDrawRangeElements.
The VBO and EBO are instanciated like this:
glGenBuffers(1, &vertex_buffer);
glGenBuffers(1, &index_buffer);
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
glBufferData(GL_ARRAY_BUFFER, vertex_buffer_size, NULL, GL_STREAM_DRAW);
glVertexAttribPointer(0,3,GL_FLOAT, GL_FALSE, 0, (char*)(NULL));
glEnableVertexAttribArray(0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, index_buffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, index_buffer_size, NULL, GL_STREAM_DRAW);
as you can see they do not have any "static" data.
I use glMapBuffer to populate the buffers and then I render them with glDrawRangeElements.
Problem:
Concretly, what I want to do is to make a terrain with Continuous LOD.
The code I use and posted majorly comes from Ranger Mk2 by Andras Balogh.
My problem is this: when I want to render the triangle strip, there seems to be a point on the 3 points of a triangle which is somewhere where it should not be.
For example,
this is what I get in wireframe mode -> http://i.stack.imgur.com/lCPqR.jpg
and this is what I get in point mode (Note the column that stretches up which is the points that are not well placed) -> http://i.stack.imgur.com/CF04p.jpg
Before you ask me to go to the post named "Rendering with glDrawRangeElements() not working properly", I wanted to let you know that I already went there.
Code:
So here is the render process:
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, index_buffer);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(4, GL_FLOAT, 0, 0);
glEnableVertexAttribArray(0);
glDrawRangeElements(GL_TRIANGLE_STRIP, 0, va_index, ia_index, GL_UNSIGNED_INT, BUFFER_OFFSET(0));
glDisableClientState(GL_VERTEX_ARRAY);
and just before I do this (pre_render function):
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, index_buffer);
vertex_array = (v4f*)(glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY));
index_array = (u32*)(glMapBuffer(GL_ELEMENT_ARRAY_BUFFER, GL_WRITE_ONLY));
//[...] Populate the buffers
glUnmapBuffer(GL_ARRAY_BUFFER);
glUnmapBuffer(GL_ELEMENT_ARRAY_BUFFER);
PS: When I render the terrain like this:
glBegin(GL_TRIANGLE_STRIP);
printf("%u %u\n", va_index, ia_index);
for(u32 i = 0; i < va_index; ++i){
//if(i <= va_index)
glVertex4fv(&vertex_array[i].x);
}
glEnd();
strangely it works (part of the triangles are not rendered though but that is another problem).
So my question is how can I make glDrawRangeElements function properly?
If you need any more information please ask, I will be glad to answer.
Edit: I use Qt Creator as IDE, with Mingw 4.8 on Windows 7. My Graphic card supports Opengl 4.4 (from Nvidia).

Answer 1

Not sure if this is causing your problem, but I notice that you have a mixture of API calls for built-in vertex attributes and generic vertex attributes.
Calls like glVertexAttribPointer, glEnableVertexAttribArray and glDisableVertexAttribArray are used for generic vertex attributes.
Calls like glVertexPointer, glEnableClientState and glDisableClientState are used for built-in vertex attributes.
You need to decide which approach you want to use, and then use a consistent set of API calls for that approach. If you use the fixed rendering pipeline, you need to use the built-in attributes. If you write your own shaders with the compatibility profile, you can use either. If you use the core profile, you need to use generic vertex attributes.
This call also looks suspicious, since it specifies a size of 3, where the rest of your code suggests that you're using positions with 4 coordinates:
glVertexAttribPointer(0,3,GL_FLOAT, GL_FALSE, 0, (char*)(NULL));