Simple oF application with GL2, GL3 and ES2 passthrough shaders on a non-power-of-two image (1024x768).

shadyApp.cpp

#include "shadyApp.h"

void shadyApp::setup() {
    ofSetBackgroundColor(ofColor::gray);
    ofSetFrameRate(60);

    image.loadImage("checkerboard.jpg"); // 1024x768

    string passthroughVertex, passthroughFragment;
#ifdef TARGET_OPENGLES
    ofLogNotice() << "ES2";
    // ES2
    passthroughVertex = "\n\
        attribute vec4 position;\n\
        attribute vec2 texcoord;\n\
        uniform mat4 projectionMatrix;\n\
        uniform mat4 modelViewMatrix;\n\
        varying vec2 varyingTexcoord;\n\
        void main() {\n\
            gl_Position = projectionMatrix * modelViewMatrix * position;\n\
            varyingTexcoord = texcoord;\n\
        }\n\
    ";
    passthroughFragment = "precision highp float;\n\
        \n\
        uniform sampler2D tex0;\n\
        varying vec2 varyingTexcoord;\n\
        void main() {\n\
            gl_FragColor = texture2D(tex0, varyingTexcoord);\n\
        }\n\
    ";
#else
    ofLogNotice() << "NOT ES2";
    if (ofIsGLProgrammableRenderer()) {
        // GL3
        passthroughVertex = "#version 150\n\
            \n\
            uniform mat4 projectionMatrix;\n\
            uniform mat4 modelViewMatrix;\n\
            in vec4 position;\n\
            in vec2 texcoord;\n\
            out vec2 varyingTexcoord;\n\
            void main() {\n\
                gl_Position = projectionMatrix * modelViewMatrix * position;\n\
                varyingTexcoord = texcoord;\n\
            }\n\
        ";
        // ??? - why gl_FragCoord.xy and not varyingTexcoord?
        passthroughFragment = "#version 150\n\
            \n\
            uniform sampler2DRect tex0;\n\
            in vec2 varyingTexcoord;\n\
            out vec4 outputColor;\n\
            void main() {\n\
                outputColor = texture(tex0, gl_FragCoord.xy);\n\
            }\n\
        ";
    } else {
        // GL2
        passthroughVertex = "#version 120\n\
            \n\
            void main() {\n\
                gl_TexCoord[0] = gl_MultiTexCoord0;\n\
                gl_Position = ftransform();\n\
            }\n\
        ";
        // ??? - why gl_FragCoord.xy and not gl_TextCoord[0].xy?
        passthroughFragment = "#version 120\n\
            \n\
            uniform sampler2DRect tex0;\n\
            void main() {\n\
                gl_FragColor = texture2DRect(tex0, gl_FragCoord.xy);\n\
            }\n\
        ";
    }
#endif
    shader.setupShaderFromSource(GL_VERTEX_SHADER, passthroughVertex);
    shader.setupShaderFromSource(GL_FRAGMENT_SHADER, passthroughFragment);
    shader.bindDefaults();
    shader.linkProgram();

    fbo.allocate(1024, 768);
    fbo.begin();
        ofClear(ofColor::black);
    fbo.end();

    string version = (char*)glGetString(GL_SHADING_LANGUAGE_VERSION);
    ofLog() << "GLSL version: " << version;
}

void shadyApp::update() {
    fbo.begin();
        // NB - skip clearing
        shader.begin();
            shader.setUniformTexture("tex0", image.getTextureReference(), image.getTextureReference().getTextureData().textureID);
            ofSetColor(ofColor::white);
            // NB - this fails to draw correctly on ES2! ofRect(0, 0, fbo.getWidth(), fbo.getHeight());
            //  possibly a manifestation of https://github.com/openframeworks/openFrameworks/issues/2593
            image.draw(0.0f, 0.0f);
        shader.end();
    fbo.end();
}

void shadyApp::draw() {
    ofSetColor(ofColor::white);
    fbo.draw(0.0f, 0.0f);
}