OpenGL - Easiest way to draw a square with a texture - c++

Question

Usually I draw a square with a texture like this:
Create a VBO with 4 coordinates (A,B,C,D for the square)
Create a EBO with 4 indices (A,C,D and B,C,D) telling that I want to draw a square out of 2 triangles.
Draw this elements with a texture
Isn't there an easiest way without having a EBO array?
Because it is not very handy to use... If I want to use like this:
VAO = [-0.8f, 0.5f, 0.0f, ...]
EBO = [0, 1, 3, 1, 2, 3, ...]
Then I need to remove a square from my VAO... then I also need to remove the indices from my EBO array and re-arrange it.
Is there a better way to do this?

Answer 1

If you really only want to draw a square with a texture on it, you should consider make a new empty VAO, and just call glDrawArrays(GL_TRIANGLE_STRIP, 0,3);
The vertex shader then looks like this:
out vec2 mapping;
void main()
{
float size = 1.0f;
vec2 offset;
switch(gl_VertexID)
{
case 0:
//Bottom-left
mapping = vec2(0.0f, 0.0f);
offset = vec2(-size, -size);
break;
case 1:
//Top-left
mapping = vec2(0.0f, 1.0f);
offset = vec2(-size, size);
break;
case 2:
//Bottom-right
mapping = vec2(1.0, 0.0);
offset = vec2(size, -size);
break;
case 3:
//Top-right
mapping = vec2(1.0, 1.0);
offset = vec2(size, size);
break;
}
gl_Position = vec4(offset, 0.0f, 1.0f);
}
The mapping variable tells the fragmentshader what the texture coordinates are.

Answer 2

Isn't there an easiest way without having a EBO array?
Duplicate your vertices & use glDrawArrays().

Answer 3

You can use DrawArray to plot the indices.
Something like this:
Vertex2D* vertex = (Vertex2D*) vbo->lock();
vertex[0].x = x[0]; vertex[0].y = y[0]; vertex[0].u = u[0]; vertex[0].v = v[0]; vertex[0].color = color;
vertex[1].x = x[0]; vertex[1].y = y[1]; vertex[1].u = u[0]; vertex[1].v = v[1]; vertex[1].color = color;
vertex[2].x = x[1]; vertex[2].y = y[1]; vertex[2].u = u[1]; vertex[2].v = v[1]; vertex[2].color = color;
vertex[3].x = x[1]; vertex[3].y = y[0]; vertex[3].u = u[1]; vertex[3].v = v[0]; vertex[3].color = color;
vbo->unlock();
shader->bind();
vbo->bind();
vao->bind();
tex->bind();
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
tex->unbind();
vao->unbind();
vbo->unbind();
shader->unbind();