在Java中手动旋转图片？

Question

I already save my image information in bitmap:

for(int j=0; j<tinggi; j++) {   
    for(int i=0; i<lebar; i++) {
        warna = pixels[j*lebar+i];
        alpha = (warna >>24) &0xff;
        red = (warna >>16) & 0xff;
        bmpR[i][j] = red;
        green = (warna >>8) &0xff;
        bmpG[i][j] = green;
        blue = blue = (warna ) &0xff;
        bmpB[i][j] = blue;
        }
    }

I try to rotate the image with this code:

for(int j=0;j<tinggi;j++) { 
    for(int i=0;i<lebar;i++) {
        double xr = (i*Math.cos(r))-(j*Math.sin(r));
        double yr = (i*Math.sin(r))+(j*Math.cos(r));
        int xro =  (int) Math.round(xr);
        int yro =  (int) Math.round(yr);
        rotationR [i+ xro][j+ yro] = (bmpR[i][j]);
        rotationG [i+ xro][j+ yro] = (bmpG[i][j]);
        rotationB [i+ xro][j+ yro] = (bmpB[i][j]);
        }
    }    

for(int j=0;j<tinggi;j++) { 
    for(int i=0;i<lebar;i++) {
        g.setColor(new Color(rotationR[i][j], rotationG[i][j], rotationB[i][j]));
        g.drawLine(i+lebar+100, j+450, i+lebar+100, j+450);
    }
}

But it doesn't output anything (While the translation and scaling is working).

What's wrong with my rotation code?

Answer 1

there is a flaw in your logic:

you have to store the new location in a array instead of changing the array indice

Point[][] rotatedLocations = ...

for(int j=0;j<tinggi;j++) { 
    for(int i=0;i<lebar;i++) {
        double xr = (i*Math.cos(r))-(j*Math.sin(r));
        double yr = (i*Math.sin(r))+(j*Math.cos(r));
        int xro =  (int) Math.round(xr);
        int yro =  (int) Math.round(yr);
        rotatedLocations[i][j] = new Point(xr, yr);
    }
}  

when you draw the pixel, draw them just on the associated location

for(int j=0;j<tinggi;j++) { 
    for(int i=0;i<lebar;i++) {

        //new (rotated) location for original x/y
        Point rotatedLocation = rotatedLocations[i][j];

        //color from the original
        g.setColor(new Color(original[i][j], original[i][j], original[i][j]));

        //but drawn on the new (rotated) location
        g.drawLine(rotatedLocation.x, rotatedLocation.y, rotatedLocation.x, rotatedLocation.y);
    }
}