Depth in shader using openFrameworks.

main.cpp

#include "ofMain.h"

class ofApp : public ofBaseApp {
public:
    ofShader shader;
    ofEasyCam cam;
    ofFbo fbo;
    void setup() {
        ofBackground(0);    
        ofFbo::Settings s;
        s.width = ofGetWidth();
        s.height = ofGetHeight();
        s.useDepth = true;
        s.depthStencilAsTexture = true;
        fbo.allocate(s);
        shader.load("shader");
    }
    void draw() {
        ofEnableDepthTest();
        fbo.begin();
        cam.begin();
        ofClear(0);
        ofSetColor(255);
        ofIcoSpherePrimitive(400, 2).draw();
        cam.end();
        fbo.end();
        ofDisableDepthTest();
        
        if(ofGetKeyPressed(' ')) {
            fbo.draw(0, 0);
        } else {
            shader.begin();
            shader.setUniformTexture("tex0", fbo.getDepthTexture(), 1);
            fbo.draw(0, 0);
            shader.end();
        }
    }
};

int main() {
    ofGLWindowSettings settings;
    settings.setSize(1920, 1080);
//    settings.setGLVersion(3,2); // GL3
    settings.setGLVersion(2,1); // GL2
    ofCreateWindow(settings);
    ofRunApp(new ofApp());
}

screenshot.png

shader.frag

// #version 150 // GL3
#version 120 // GL2

const float near = 0.9835;
const float range = .005;

uniform sampler2DRect tex0;

// in vec2 texCoordVarying; // GL3
// out vec4 outputColor; // GL3
varying vec2 texCoordVarying; // GL2

void main (void) {
    // float depth = texture(tex0, texCoordVarying).r; // GL3
    float depth = texture2DRect(tex0, texCoordVarying).r;
    float b = (depth - near) / range;
    // outputColor = vec4(b,b,b,1.); // GL3
    gl_FragColor = vec4(b,b,b,1.); // GL2
}

shader.vert

// #version 150 // GL3
#version 120 // GL2

uniform sampler2DRect tex0;

// uniform mat4 modelViewProjectionMatrix; // GL3
// in vec4 position; // GL3
// in vec2 texcoord; // GL3
// out vec2 texCoordVarying; // GL3
varying vec2 texCoordVarying; // GL2

void main() {
    // gl_Position = modelViewProjectionMatrix * position; // GL3
    // texCoordVarying = texcoord; // GL3
    
    texCoordVarying = gl_MultiTexCoord0.xy; // GL2
    gl_Position = ftransform(); // GL2
}