2D Texture morph in Ortographic Projection

Question

I'm having a hard time figuring out what's going on with my texture:

Basically I am fetching a webcam stream as my underlying 2d texture canvas in OpenGL, and in my paintGL() I'm drawing stuff on it (as RGBA images with GL_BLEND). Since I'm using a Kinect as a data source, I'm also getting the depth values from a tracked skeleton (a person), and converting them into GL values (XYZ varying between 0.0f and 1.0f). So my goal is that, for instance, a loaded 2D Texture like a shirt, is now properly tracking the person in my RGB output display. But it seems my understanding of orthographic projection is wrong:

I'm constantly loading the 4 converted vertices into a VBO, but whenever I put the texture on top of this dynamic quad, it's always facing the screen. I thought that putting this dynamic quad between the "background" canvas and the camera would result in a proper projection of the quad onto the canvas, which would give me the impression of a warping 2D texture, that seems to "bend" whenever the person rotates.

But the texture is always facing the camera and doesnt rotate. I've also tried to manually rotate via a matrix and set that into my shader, but again, it only rotates the vertice quad itself (as: rotation simply makes the texture smaller) , and THEN puts the texture on top, instead of rotating the texture with it.

So, is it somehow possible to properly apply this to the texture? I've thought about mixing a perspective projection in, but actually have no idea how to implement this...

EDIT: I've actually already set my projection matrix up like the following:

In resizeGL():

projection.setToIdentity();
projection.ortho(0.0f, 1.0f, 0.0f, 1.0f, 2.0f, -5.0f);
projection.translate(0.0f, 0.0f, 3.0f);

In paintGL():

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glDisable(GL_DEPTH_TEST);  // turning this on/off makes no difference
glEnable(GL_TEXTURE_2D);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, &textureID);

program.setUniformValue("mvp_matrix", projection);
program.setUniformValue("texture", 0);
//draw 2d background quad
drawQuad();

glClear(GL_DEPTH_BUFFER_BIT);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

// switch to frustum to give perspective view
projection.setToIdentity();
projection.frustum(0.0f, 1.0f, 0.0f, 1.0f, 2.0f, -5.0f);
projection.translate(0.0f, 0.0f, 3.0f);

// bind cloth texture and draw ontop 2d quad
clothTexture->bind();
program.setUniformValue("mpv_matrix", projection);
drawShirtQuad();

// reset to ortho view
projection.setToIdentity();
projection.ortho(0.0f, 1.0f, 0.0f, 1.0f, 2.0f, -5.0f);

// release texture
clothTexture->release();
glDisable(GL_BLEND);

clothTexture is a QOpenGLTexture that has successfully loaded an RGBA image from a file. Result: whenever I activate the frustum perspective, it results in a black screen. I think everything is correctly set up: POV is traversed towards positive z-axis in resizeGL(), and all the cloth vertices vary between 0 and 1 in XYZ, while the background is positioned at:

(0.0f, 0.0f, -1.0f), (1.0f, 0.0f, -1.0f), (1.0f, 1.0f, -1.0f), (0.0f, 1.0f, -1.0f).

So the cloth object is always positioned between background plane and POV. Am i missing something in the frustum setup ? I've simply set it up the same way as ortho...

EDIT: Sorry for not mentiong; the matrix I'm using is a QMatrix4x4 type: Frustum

These functions multiply the current matrix with the one you define as an argument, which should yield the same result as if I define a View matrix for instance, and then define my shader uniform "mvp_matrix" as projection * view, if I'm not mistaken. Maybe something like lookAt will do the trick; I'll just try messing around more. :)

Ramil Kudashev Ramil Kudashev · Accepted Answer · 2015-10-07T14:07:20

You need to use a perspective projection to achieve desired result. Look here for example code for perspective projection matrix creation with glm.

Moving vertices wouldn't be needed as you will get proper positions with rotation applied in your model matrix.

EDIT: in your code where can i look at .frustum and .translate methods or from what library projection object is? It doesn't look like you are doing Projection * View by moving frustum matrix. Some info about roles of standard matrices.

Considering debugging if you get on screen black color instead of GL_COLOR_BUFFER_BIT color problem is not with matrix but earlier. Also i recommend to console.log your perspective matrix and compare it to correct one (which you can get for example in glm library).

2D Texture morph in Ortographic Projection

1 Answers