Draw ofImage.getTexture in shader in wrong orientation


When I try to draw ofImage texture in shader, it draws the image in a wrong orientation, like only uv rotated -90 degrees, not the entire pixels of the image.

  • original image

  • seems only uv is wrong cause image’s ratio seems correct

  • when uv is rotated 90 degs

I thought it’s some sort of a horizontal&landscape profile in a metadata of pics cause I was using an image taken from iphone. However, it still happens when I use random images created from photoshop or so.

Maybe I was drawing a quad in a wrong order? or passing the uv in a wrong way in vertex shader? Any thoughts are much appreciated.

Here’s the code, you can reproduce the situation by commenting out 2 lines that I indicate below.

#define GLSL(version, shader)  "#version " #version "\n" #shader
ofImage image;
ofShader shader;

void ofApp::setup(){
    std::string vert = GLSL(120,
        varying vec2 texCoord;
        void main(){
            gl_Position = gl_ProjectionMatrix * gl_ModelViewMatrix * gl_Vertex;
            texCoord = gl_MultiTexCoord0.xy;
    std::string frag = GLSL(120,
        uniform sampler2D image;
        varying vec2 texCoord;
        void main(){
           vec2 uv = texCoord;

            // so I had to rotate uv 90 degs here to display the image in a right orientation. but why?
            // you can comment out following 2 lines to reproduce the situation
            uv = vec2((uv.x-.5),uv.y-.5)*mat2(cos(1.5708),sin(1.5708),-sin(1.5708),cos(1.5708));
            uv += vec2(.5);

            vec3 c = texture2D(image, uv).rgb;
            gl_FragColor = vec4(c, 1.);
    shader.setupShaderFromSource(GL_VERTEX_SHADER, vert);
    shader.setupShaderFromSource(GL_FRAGMENT_SHADER, frag);

void ofApp::draw(){
        shader.setUniformTexture("image", image.getTexture(), 0);
        float _w = image.getWidth(), _h = image.getHeight();
            glVertex3f( 0,  0, 0), glTexCoord2f(  0,   0);
            glVertex3f( 0, _h, 0), glTexCoord2f(  0, 1.f);
            glVertex3f(_w, _h, 0), glTexCoord2f(1.f, 1.f);
            glVertex3f(_w,  0, 0), glTexCoord2f(1.f,   0);