ofImage::setFromPixels() causes crash on iOS

bugs, errors
#1

Hi, I just figured out calling ofImage::setFromPixels() causes crash on iOS while it works fine on MacOS.

Here’s my test code.

ofFbo fbo;
ofImage img;

//--------------------------------------------------------------
void ofApp::setup(){

    ofSetBackgroundColor(0);
    
    //allocate an image space
    img.allocate(ofGetWidth(), ofGetHeight(), OF_IMAGE_COLOR_ALPHA);
    
    //clear and allocate a fbo
    fbo.begin();
    ofClear(0,0,0,0);
    fbo.end();
    fbo.allocate(ofGetWidth(), ofGetHeight(), GL_RGBA);
    
    //draw an ellipse to the fbo
    fbo.begin();
    ofClear(0,0,0,0);
    ofSetColor(255);
    ofDrawEllipse(ofGetWidth()/2, ofGetHeight()/2, ofGetWidth(), ofGetHeight());
    fbo.end();
    
    //copy pixels from fbo to image
    ofPixels pixels;
    fbo.getTexture().readToPixels(pixels);
    img.setFromPixels(pixels);
}

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

//--------------------------------------------------------------
void ofApp::draw(){
    
    //draw the image
    img.draw(0, 0, ofGetWidth(), ofGetHeight());
}

And this is the result you will see if you run the code on MacOS.

Screen Shot 2017-10-27 at 12.07.02 AM.png800×638 7.62 KB

However, if you run the same code on iOS, it crashes on startup with the following error.

Screen Shot 2017-10-27 at 12.08.43 AM.png2880×1752 1.32 MB

It doesn’t produce any error if I comment out img.setFromPixels(pixels);

Should I report this on github?
And Is there any other way to copy pixels from ofFbo to ofImage?
Thanks!

#2

Hi! The app I work on does that successfully on iOS. But we allocate using OF_PIXELS_RGBA (=4) instead of OF_IMAGE_COLOR_ALPHA (=0x02).

Oh wait, I got confused: your pixels are actually not allocated. I was looking at img above. Maybe that’s the reason?

#3

Hi, @hamoid

I added pixels.allocate(ofGetWidth(), ofGetHeight(), OF_PIXELS_RGBA); after ofPixels pixels;

And it no longer crashed but I cannot see the white ellipse and all I see is just a black screen.

Is it necessary to allocate ofPixels before calling ofTexure::readToPixels()?
Shouldn’t this method internally allocate the size too?

#4

Not sure if it should be allocated automatically. I just look at how it’s done in the app I’ve been working on since last year.

I remember another issue: we don’t initialize things inside setup, instead we do this:

// update
if(ofGetFrameNum() == 5) {
  // my setup stuff
}

It looks silly, but it fixed some initialization issues with FBOs. This is what I wrote in a commit on June 1st: “Delay setup for a few frames. Delaying setup might help on iOS with FBOs”.

See Fbo.begin() inside setup breaks rendering on iOS

#5

Thanks for the tip.
I tried it but it didn’t fix the problem.

#6

Could you show your updated code?

#7 
//--------------------------------------------------------------
void ofApp::setup(){	

    ofSetBackgroundColor(0);
}

//--------------------------------------------------------------
void ofApp::update(){
    
    if (ofGetFrameNum() == 5) {
     
        //allocate an image space
        img.allocate(ofGetWidth(), ofGetHeight(), OF_IMAGE_COLOR_ALPHA);
        
        //clear and allocate a fbo
        fbo.begin();
        ofClear(0,0,0,0);
        fbo.end();
        fbo.allocate(ofGetWidth(), ofGetHeight(), GL_RGBA);
        
        //draw an ellipse to the fbo
        fbo.begin();
        ofClear(0,0,0,0);
        ofSetColor(255);
        ofDrawEllipse(ofGetWidth()/2, ofGetHeight()/2, ofGetWidth(), ofGetHeight());
        fbo.end();
        
        //copy pixels from fbo to image
        ofPixels pixels;
        pixels.allocate(ofGetWidth(), ofGetHeight(), OF_PIXELS_RGBA);
        fbo.getTexture().readToPixels(pixels);
        img.setFromPixels(pixels);
    }
}

//--------------------------------------------------------------
void ofApp::draw(){

    if (ofGetFrameNum() > 5) {
    
        //draw the image
        img.draw(0, 0, ofGetWidth(), ofGetHeight());
    }
}

This doesn’t crash but doesn’t draw properly as I said.
if you remove pixels.allocate(ofGetWidth(), ofGetHeight(), OF_PIXELS_RGBA); it still crashes.

#8

I would not call ofClear() before allocating the fbo. But I don’t know what can be the issue :confused:

#9

I tried it but didn’t help either… :disappointed:

#10

I just tested this on Android and the same problem occurred.
Just like on iOS, It crashes when calling img.setFromPixels(pixels);
And if I add pixels.allocate(ofGetWidth(), ofGetHeight(), OF_PIXELS_RGBA); after ofPixels pixels; it doesn’t crash but doesn’t draw properly. All I see is a black screen.

#11

What about your main.mm file? Ours:

    //  here are the most commonly used iOS window settings.
    //------------------------------------------------------
    ofiOSWindowSettings settings;
    settings.enableRetina = true; // enables retina resolution if the device supports it.
    settings.enableDepth = false; // enables depth buffer for 3d drawing.
    settings.enableAntiAliasing = false; // enables anti-aliasing which smooths out graphics on the screen.
    settings.numOfAntiAliasingSamples = 4; // number of samples used for anti-aliasing.
    settings.enableHardwareOrientation = true; // enables native view orientation.
    settings.enableHardwareOrientationAnimation = true; // enables native orientation changes to be animated.
    settings.glesVersion = OFXIOS_RENDERER_ES2; // type of renderer to use, ES1, ES2, etc. we need es2 for IMGui
    //ofCreateWindow(settings);

    ofAppiOSWindow * window = (ofAppiOSWindow *)(ofCreateWindow(settings).get());
#12

Hey Thanks for your help @hamoid

I could fix the problem by changing fbo.getTexture().readToPixels(pixels); to fbo.readToPixels(pixels); on iOS.

It also fixed the problem on Android.
Thanks for help!

https://github.com/openframeworks/openFrameworks/issues/5790

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