My textured shape has a crease along the hypotenuse of my quad. How do i prevent this?

Core Library Questions

xeracy

My textured shape has a crease along the hypotenuse of my quad. How do i prevent this?

in Core Library Questions • 1 year ago

I am drawing trapezoidal parts of a shape and while the the top and bottom seem so have no problems, the sides seem to be constructed from triangles and not quads. Btw, this was based on the 'textured cube" example.

EDIT: Added Screen Shot.

This screen shot is from 2.06a on Windows 7.

beginShape(QUADS);
texture(tex);

//top
vertex(-2, 2, -4, 0, 0);
vertex( 2, 2, -4, 1, 0);
vertex( 4, 4, 0, 1, 1);
vertex(-4, 4, 0, 0, 1);

// mid
vertex(-2, -2, -4, 0, 0);
vertex( 2, -2, -4, 1, 0);
vertex( 2, 2, -4, 1, 1);
vertex(-2, 2, -4, 0, 1);

//bott.
vertex(-4, -4, 0, 0, 0);
vertex( 4, -4, 0, 1, 0);
vertex( 2, -2, -4, 1, 1);
vertex(-2, -2, -4, 0, 1);

// left -- HAS A CREASE FROM CORNER TO CORNER
vertex(-4, -4, 0, 0, 0);
vertex(-2, -2, -4, 1, 0);
vertex(-2, 2, -4, 1, 1);
vertex(-4, 4, 0, 0, 1);

// right -- HAS A CREASE FROM CORNER TO CORNER
vertex( 2, -2, -4, 0, 0);
vertex( 4, -4, 0, 1, 0);
vertex( 4, 4, 0, 1, 1);
vertex( 2, 2, -4, 0, 1);

endShape();

I can post the rest of the program if anyone thinks its necessary or easier to debug ( I am trying to recreate David Ope's black and white GIFs.)

Replies(6)

xeracy

Re: My textured shape has a crease along the hypotenuse of my quad. How do i prevent this?

1 year ago

might as well post all the code:

PImage tex;
float rotx = 0;//
float roty = 0;//;
int f = 1;

void setup() {
size(500, 500, P3D);
colorMode(HSB, 100);
tex = createImage(100, 100, ARGB);
textureMode(0);
background(0);

}

void draw() {
background(0);
int offCount = f * tex.height;
int pixCount = 0;
boolean t = false;
tex.loadPixels();
//println("__Begin__" + (f * tex.height));
for(int i = 0; i < tex.width; i++) {

    for(int j = 0; j < tex.height; j++) {
      if(pixCount % (10 * tex.width) == 0) {
        t = !t;
      }
      if(offCount < tex.pixels.length) {
        tex.pixels[offCount] = color(0,0,int(t)*100,int(t)*100);
        //print(offCount + ",");
      } else {
        tex.pixels[offCount - tex.pixels.length] = color(0,0,int(t)*100,int(t)*100);
        //print((offCount - pixCount) + ";");
      }
      //print(pixCount + "/" + offCount + " ");
      pixCount++;
      offCount++;
    }
    //println();
}

// println("__End__");
tex.updatePixels();
f++;
if (f > 20) f = 1;
//image(tex,0,0);

noStroke();
translate(width/2.0, height/2.0, -100);
rotateX(rotx);
rotateY(roty);
scale(90);
TexturedCube(tex);
}

void TexturedCube(PImage tex) {
beginShape(QUADS);
texture(tex);

//top
vertex(-2, 2, -4, 0, 0);
vertex( 2, 2, -4, 1, 0);
vertex( 4, 4, 0, 1, 1);
vertex(-4, 4, 0, 0, 1);

// mid
vertex(-2, -2, -4, 0, 0);
vertex( 2, -2, -4, 1, 0);
vertex( 2, 2, -4, 1, 1);
vertex(-2, 2, -4, 0, 1);

//bott.
vertex(-4, -4, 0, 0, 0);
vertex( 4, -4, 0, 1, 0);
vertex( 2, -2, -4, 1, 1);
vertex(-2, -2, -4, 0, 1);

// left
vertex(-4, -4, 0, 0, 0);
vertex(-2, -2, -4, 1, 0);
vertex(-2, 2, -4, 1, 1);
vertex(-4, 4, 0, 0, 1);

// right
vertex( 2, -2, -4, 0, 0);
vertex( 4, -4, 0, 1, 0);
vertex( 4, 4, 0, 1, 1);
vertex( 2, 2, -4, 0, 1);

endShape();
}

PhiLho

Re: My textured shape has a crease along the hypotenuse of my quad. How do i prevent this?

1 year ago

Actually, it looks perfect on my computer: Windows 7, Java 1.6.0_30, Processing 1.5.1.
A bit less perfect in OpenGL mode.

xeracy

Re: My textured shape has a crease along the hypotenuse of my quad. How do i prevent this?

1 year ago

ahh.. im using 2.06a... maybe its just an issue with the latest 2.0 alpha.

So... now what, lol? do i need to report this as a bug for 2.06a? I guess i could use an 1.5.1, but i'll have to see if the speed will be an issue.

Thanks PhiLho!

amnon.owed

Re: My textured shape has a crease along the hypotenuse of my quad. How do i prevent this?

1 year ago

Depending on what you want, it seems your texture coordinates for left and right are off.

You could use something like below or any variation of the 1001 or 0110 texture coordinates.

// left
vertex(-4, -4, 0, 0, 0);
vertex(-2, -2, -4, 1, 1);
vertex(-2, 2, -4, 1, 1);
vertex(-4, 4, 0, 0, 0);
// right
vertex( 2, -2, -4, 0, 1);
vertex( 4, -4, 0, 1, 0);
vertex( 4, 4, 0, 1, 0);
vertex( 2, 2, -4, 0, 1);

xeracy

Re: My textured shape has a crease along the hypotenuse of my quad. How do i prevent this?

1 year ago

amnon.owed,

that rotated the texture, but it looks correct as far as the texture not being distorted. I still cant seem to get it rotated correctly and not have the seam. Here is what i am trying to duplicate.

After a little googling, i found this on wikipedia:

Because affine texture mapping does not take into account the depth information about a polygon's vertices, where the polygon is not perpendicular to the viewer it produces a noticeable defect.

http://en.wikipedia.org/wiki/Texture_mapping#Perspective_correctness

the image on the wiki page shows the problem im having. This means that the texture mapping method in processing is affine? is this a result of me trying to force perspective on my 'shape' with a z-dimension? (which is fully intentional)

amnon.owed

Re: My textured shape has a crease along the hypotenuse of my quad. How do i prevent this?

1 year ago

There may be something going on like that. With certain combinations it keeps giving distortions. When you make it a 'normal' quad the distortion disappears. So it's some combinations of coordinates and perspective.

There may be alternative solutions (without textures) to recreate that effect though. For example directly through shapes or rects. Or even purely 2D.

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