glDrawElements problem

OpenGL OpenGL: Advanced Coding
1

Hello :slight_smile: i have strange problem with this command :slight_smile: it just doesn’t show anything and i really do¨n’t know why.

this is filling buffer with data.

 
    this->TerrainLOD1[0] = 0;
	this->TerrainLOD1[1] = 0;
	this->TerrainLOD1[2] = 0;

	this->TerrainLOD1[3] = 2;
	this->TerrainLOD1[4] = 0;
	this->TerrainLOD1[5] = 0;

	this->TerrainLOD1[6] = 2;
	this->TerrainLOD1[7] = 0;
	this->TerrainLOD1[8] = 2;

	this->TerrainLOD1[9] = 0;
	this->TerrainLOD1[10] = 0;
	this->TerrainLOD1[11] = 2;

    
	this->TerrainLOD1_INDICES[0] = 0; 
	this->TerrainLOD1_INDICES[1] = 1; 
	this->TerrainLOD1_INDICES[2] = 2;

	this->TerrainLOD1_INDICES[3] = 0; 
	this->TerrainLOD1_INDICES[4] = 3; 
	this->TerrainLOD1_INDICES[5] = 2;

	glGenBuffers(1, &this->VBO_BUFFER_ID1);
	glBindBuffer(GL_ARRAY_BUFFER, this->VBO_BUFFER_ID1);
	glBufferData(GL_ARRAY_BUFFER, sizeof(TerrainLOD1), TerrainLOD1, GL_STATIC_DRAW);
                        

	glGenBuffers(1, &this->VBO_BUFFER_ID1_INDICES);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this->VBO_BUFFER_ID1_INDICES);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(TerrainLOD1_INDICES), TerrainLOD1_INDICES, GL_STATIC_DRAW);

This is drawing part. When i uncommend glBegin - glend … it shows an triangle. i wanted to avoid bad camera angle or similar.

 
	glPushMatrix();
    //glTranslatef(x,y,z);
	
    
	glBindBuffer(GL_ARRAY_BUFFER, TerrainManager::TERRAIN->VBO_BUFFER_ID1);
    glVertexPointer(3, GL_FLOAT, 0 , 0);

    glEnableClientState(GL_VERTEX_ARRAY);

	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, TerrainManager::TERRAIN->VBO_BUFFER_ID1_INDICES);	
	glIndexPointer(GL_UNSIGNED_SHORT, 0, 0);

	glEnableClientState(GL_INDEX_ARRAY);   	

    
	glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

	glDisableClientState(GL_INDEX_ARRAY);
	glDisableClientState(GL_VERTEX_ARRAY);

    glBindBuffer(GL_ARRAY_BUFFER, NULL);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, NULL);	

    /*
    glBegin(GL_TRIANGLES);
		glVertex3f(0,0,0);
		glVertex3f(2,0,0);
		glVertex3f(2,0,2);
	glEnd();
    */

	glPopMatrix();

What’s bad on this code ? Thank yo uvery much

2

You store indices as GL_UNSIGNED_SHORT (see glIndexPointer) while trying to draw them as GL_UNSIGNED_INT (see glDrawElements).

3

Thanks for reply.

I tried to set both to GL_UNSIGNED_SHORT or GL_UNSIGNED_INT … but still, window is black as a hell :smiley:

4

Show your his->TerrainLOD1 and this->TerrainLOD1_INDICES declaration, please.

BTW, have you got the code from the sky or went into the problem iteratively? do you have a version that draws something? a line?

5

lol, i got it.

I filled index buffer with FLOATS, but i read it as INTs … damn. Pretty stupid error.

Thanks for helping :slight_smile: