CODEWITHSUNDEEP
c++openglopengl-es
user1997675
user1997675

Reputation: 144

Modern OpenGL 3.0: How to move a 2D vbo on screen

I have been learning modern OpenGL (3.0) for a couple of weeks now and am trying to create a lunar lander clone in 2D. All tutorials and questions I have read so far did not help at all.

Vertexes in header and other OpenGL:

GLuint vertexArrayLander;
GLuint landerVBO;
GLfloat landerVertex [26] = {

        //Lander Body
           0.03f, 0.2f,
          (-0.03f), 0.2f,
          (-0.05f), 0.15f,
          (-0.05f), 0.1f,
          (-0.03f), 0.05f,

          (-0.045f), 0.0f,      //left leg
          (-0.029f), 0.05f,

          (0.029f), 0.05f,      //right leg
          (0.045f), 0.0f,

          0.03f, 0.05f,     
          0.05f, 0.1f,      
          0.05f, 0.15f,     
          0.03f, 0.2f

};

Constructor:

Lander::Lander() {    
glGenVertexArrays(1, &vertexArrayLander);
glBindVertexArray(vertexArrayLander);

glGenBuffers(1, &landerVBO);    
glBindBuffer(GL_ARRAY_BUFFER, landerVBO);   
glBufferData(GL_ARRAY_BUFFER, sizeof(landerVertex), landerVertex,GL_STATIC_DRAW);
 }

Drawing works so far, but how do I apply x and y to my landerVbo without messing with the array directly? I have tried using glTranslatef(x,y,0.0f) which had no effect at all.

Drawing Method:

void Lander::drawLander() {
float x = position->getX();
float y = position->getY();

glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, landerVBO);
glVertexAttribPointer(0,           // attribute 0. No particular reason.
        2,                  // size
        GL_FLOAT,           // type
        GL_FALSE,           // normalized?
        0,                  // stride
        (void*) 0            // array buffer offset
        );


//draw all graphic elements

//How to apply x and y on all points?

glDrawArrays(GL_LINE_STRIP, 0 , 13);
//vao

glDisableVertexAttribArray(0);
}

x and y are the position of the lander on screen. What I want to draw is this pseudo code:

GLfloat landerVertex [26] = {

        //Lander Body
          x + 0.03f, y + 0.2f,
          x + (-0.03f), y + 0.2f,
          x + (-0.05f), y + 0.15f,
          x + (-0.05f), y + 0.1f,
          x + (-0.03f), y + 0.05f,

          x + (-0.045f), y + 0.0f,      //left leg
          x + (-0.029f), y + 0.05f,

          x + (0.029f), y + 0.05f,      //right leg
          x + (0.045f), y + 0.0f,

          x + 0.03f, y + 0.05f,     
          x + 0.05f, y + 0.1f,      
          x + 0.05f, y + 0.15f,     
          x + 0.03f, y + 0.2f

};

Upvotes: 0

Views: 719

Answers (1)

FToDance
FToDance

Reputation: 315

  • Trying to use the fixed pipeline (no shaders), is no longer recommended, but is still possible (the GPU's emulate it).
  • You can still use opengl 1 syntax (glTranslatef etc)
  • Before glDrawArrays. You will need to setup the appropriate matrices as always.
  • Normally they are done by the user specifying their own model/view/projection matrices, and sending them to a shader to compute the output. The mesh data for static meshes is generally not touched (so you can reuse it etc..)

Upvotes: 1

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