How to rotate a bitmap around center without clipping

[samavr]

How can I rotate a bitmap around its center without clipping the corners?

I have increased the size using

GD.BitmapSize(NEAREST, BORDER, BORDER, 189, 188);

and I use this function to rotate

static void rotate(uint16_t a)
{
 GD.cmd_translate(F16(64), F16(64));
 GD.cmd_rotate(a);
 GD.cmd_translate(F16(-64), F16(-64));
}


However, still one corner gets clipped.

[tftlcdcyg]

The size that you must increase is the background of the base image, with the help of some image editing program and that allows you to preserve transparencies in case it is a png image; keeping it centered all the time, this way no part of the image will be cut off when rotated

[samavr]

I use FT800, I think it does not support transparency, however now I use JPG with the black background

[tftlcdcyg]

With GRAM size limits of the screen, you could use the gd2asset tool to be able to process png images.

[jamesbowman]

Hi samavr ,


I assume the bitmap size is 128x128, to avoid corner clipping, you need to make the size a couple of pixels bigger than 128*sqrt(2):


GD.BitmapSize(NEAREST, BORDER, BORDER, 184, 184);


then use this function to rotate


static void rotate(uint16_t a)
{
 GD.cmd_translate(F16(184/2), F16(184/2));
 GD.cmd_rotate(a);
 GD.cmd_translate(F16(-64), F16(-64));
}
Taking the transforms in reverse order:

• the first one moves the original 128x128 bitmap so its center is at (0,0)
• rotate the bitmap
• move the bitmap so its center is at (92,92)

You will see some shimmer in the bitmap due to NEAREST sampling. If you change the BitmapSize to:

GD.BitmapSize(BILINEAR, BORDER, BORDER, 184, 184);

it will look smooth as it rotates.