topic PXP Rotation setup in i.MX RT Crossover MCUs

PXP Rotation setup

mborgerson — Fri, 27 Jan 2023 17:28:01 GMT

I am trying to set up the PXP to perform a 90-degree rotation of an input image with dimensions of 480 x 320 pixels in RGB565 format. I do not get the desired results with the following processed surface and output setup:

OUT_PITCH: 960 OUT_LRC: 479,319 // OUT_ULC assumed to be 0,0
OUT_PS_ULC: 0, 0 OUT_PS_LRC: 479,319

If I start with an image with 320 x 320 dimensions, I do get a successful rotation.

A PXP rotation example from the SDKs has the following cryptic code:

#define APP_IMG_WIDTH WIDTH 480 // my own image definitions

#define APP_IMG_HEIGHT HEIGHT 320

/* PS input buffer is square. */ Why did they use a square--was it not designed to rotate the whole input image??

#if APP_IMG_WIDTH > APP_IMG_HEIGHT // from the SDK example

#define APP_PS_SIZE APP_IMG_HEIGHT

#else

#define APP_PS_SIZE APP_IMG_WIDTH

#endif

#define APP_PS_ULC_X ((APP_IMG_WIDTH / 2) - (APP_PS_SIZE / 2))

#define APP_PS_ULC_Y ((APP_IMG_HEIGHT / 2) - (APP_PS_SIZE / 2))

#define APP_PS_LRC_X ((APP_IMG_WIDTH / 2) + (APP_PS_SIZE / 2) - 1U)

#define APP_PS_LRC_Y ((APP_IMG_HEIGHT / 2) + (APP_PS_SIZE / 2) - 1U)

If I use these defines, I get the following register setup before the rotation:

OUT_PITCH: 960 OUT_LRC: 479,319
OUT_PS_ULC: 80, 0 OUT_PS_LRC: 399,319

Now the OUT_PS corners are a square in the middle of the desired image. This does not seem to be a good recipe for rotating a complete rectangular image! There are fewer pixels in the OUT_PS boundaries than there are in the output image.

I've got a pretty good understanding of the PXP capabilities for scaling, offsetting and blending images and was able to write an app to do a slide show with slide-in, zoom in, fade out, and other transitions as well as a Ken-Burns display of an image (slow zoom and offsets).

Rotation remains a mystery. The text in the PXP section Rev3 of the IMXRT1023 reference manual is helpful, but does not have any particular detail on the setup of the PXP for rotation.

Re: PXP Rotation setup

jingpan — Wed, 01 Feb 2023 08:11:43 GMT

Hi @mborgerson ,

I modify the pxp_rotate example to rotate a rectangle. Please take a look.

Regards,

Jing

Re: PXP Rotation setup

mborgerson — Sat, 04 Feb 2023 16:36:25 GMT

Unfortunately, while the changes may rotate the full image rectangle, the code still has all the defines with no explanation:

#define APP_IMG_WIDTH  DEMO_BUFFER_WIDTH     //480
#define APP_IMG_HEIGHT DEMO_BUFFER_HEIGHT    //272

/* PS input buffer is not square. */
#if APP_IMG_WIDTH > APP_IMG_HEIGHT
#define APP_PS_WIDTH APP_IMG_HEIGHT      //272
#define APP_PS_HEIGHT (APP_IMG_HEIGHT/2+8)      //272

#else
#define APP_PS_SIZE APP_IMG_WIDTH
#endif

#define APP_PS_ULC_X ((APP_IMG_WIDTH / 2) - (APP_PS_WIDTH / 2))
#define APP_PS_ULC_Y ((APP_IMG_HEIGHT / 2) - (APP_PS_HEIGHT / 2))
#define APP_PS_LRC_X ((APP_IMG_WIDTH / 2) + (APP_PS_WIDTH / 2) - 1U)
#define APP_PS_LRC_Y ((APP_IMG_HEIGHT / 2) + (APP_PS_HEIGHT / 2) - 1U)

#define APP_PS_ULC_X1 ((APP_IMG_WIDTH / 2) - (APP_PS_HEIGHT / 2))
#define APP_PS_ULC_Y1 ((APP_IMG_HEIGHT / 2) - (APP_PS_WIDTH / 2))
#define APP_PS_LRC_X1 ((APP_IMG_WIDTH / 2) + (APP_PS_HEIGHT / 2) - 1U)
#define APP_PS_LRC_Y1 ((APP_IMG_HEIGHT / 2) + (APP_PS_WIDTH / 2) - 1U)

What is needed is an explanation of why these #define statements are part of the code.

In my own experiments, I get good result by just setting the PS corners to (0,0) and (width-1, height-1). I set the output surface to the same dimensions because the reference manual tells me so:

36.6.7 Output Surface Lower Right Coordinate (PXP_OUT_LRC)

This register contains the size, or lower right coordinate, of the output buffer NOT rotated. It is implied that the upper left coordinate of the output surface is always [0,0]. When rotating the framebuffer, the PXP will automatically swap the X/Y, or WIDTH/ HEIGHT, to accomodate the rotated size.