Rendering slow when looking at entire mesh

@leodok wrote:

Hey, so I'm fairly new to oF and C++ and have the following code, my aim is to generate some simple terrain and render it.

For some reason, when I look at a small section of the mesh, it renders lightning fast, but if I try to look at the entire thing it becomes really slow....
What's going on ?

#include "ofApp.h"

void ofApp::generateTerrain() {
	mesh.clearVertices();
	xoff -= ((t_w - 1)*off_increment);
	int numTris = 0;
	for (int x = 0; x < t_w; x++) {
		for (int y = 0; y < t_w; y++) {

			float z = ofNoise(xoff, yoff)*zheight;
			mesh.addVertex(ofVec3f(ofPoint(x*seperation, y*seperation, z)));

			z = ofNoise(xoff, yoff + off_increment)*zheight;
			mesh.addVertex(ofVec3f(ofPoint(x*seperation, (y + 1)*seperation, z)));

			z = ofNoise(xoff + off_increment, yoff) * zheight;
			mesh.addVertex(ofVec3f(ofPoint((x + 1)*seperation, y*seperation, z)));

			mesh.addTriangle(numTris * 3, numTris * 3 + 1, numTris * 3 + 2);
			numTris++;

			mesh.addVertex(ofVec3f(ofPoint((x + 1)*seperation, y*seperation, z)));

			z = ofNoise(xoff + off_increment, yoff + off_increment) * zheight;
			mesh.addVertex(ofVec3f(ofPoint((x + 1)*seperation, (y + 1)*seperation, z)));

			z = ofNoise(xoff, yoff + off_increment) * zheight;
			mesh.addVertex(ofVec3f(ofPoint(x*seperation, (y + 1)*seperation, z)));

			mesh.addTriangle(numTris * 3, numTris * 3 + 1, numTris * 3 + 2);
			numTris++;

			yoff += off_increment;
		}
		yoff -= (t_h*off_increment);
		xoff += off_increment;
	}
}

//--------------------------------------------------------------
void ofApp::setup() {
	mesh.setMode(OF_PRIMITIVE_TRIANGLES);
	t_w = 50;
	t_h = 50;

	seperation = 100;
	xoff = 0.0f;
	yoff = 0.0f;
	off_increment = 0.1f;

	zheight = 200;

	generateTerrain();
}

//--------------------------------------------------------------
void ofApp::update(){
	generateTerrain();
}

//--------------------------------------------------------------
void ofApp::draw(){
	cam.begin();
		mesh.draw();
	cam.end();
}

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