Sorry, I tried to be generic but it did not help
So, let's explain what I try do do. In the coming sentences, I will probably write a lot of nonsense, feel free to fix me.
: Meowbit (with TFT screen), but may be applicable to any board with a screen.
- Most of their boards are relatively powerful (CPU/Bus... around 50-100MHz) but most of them have very little RAM (arounf 100K).
- Contrary to computers, everything is I/O, no memory map, no VBL/HBL/interrupts, no blitter... so LCD controller framebuffer cannot be easily used by the MCU.
, the framebuf.FrameBuffer MicroPython class is multiple things:
- a software framebuffer (as the real one cannot be used as is) to be used by program and which will eventually be sent to replace the real framebuffer.
- a helper to provide some high level operations (pixels, lines, rect, scroll...).
- a way to save RAM by implementing in software low level resolution compared to the TFT.
- more or less decoupled from LCD specs, the driver will convert the Framebuffer to the supported modes (resolution, pixel encoding, pixel organization...).
- if your goal is blitting speed and not RAM, use a framebuf as similar as the real framebuffer specs.
- if your goal is to save memory, use an smaller framebuf (grayscale, palette-indexed,...) and the driver will do the job (at a CPU cost).
So to achieve this goal
, I modified the framebuf C implementation (https://github.com/KittenBot/micropytho ... framebuf.c
) to support 2 new modes:
- PAL16 (4bit per pixel, 16 colors available, multiple hardcoded palettes selectable (C64, Spectrum,...))
- PAL256 (8bit per pixel, 256 colors available, multiple hardcoded palettes selectable (MSX,...))
In this case , the bytearray attached to the Framebuf is smaller than the TFT 160x128x16bits real framebuffer size (Meowbit init mode for the ST)
Then I modified the screen.c (https://github.com/KittenBot/micropytho ... 2/screen.c
) file which implements the driver for the ST used by the Meowbit:
When calling pyb.SCREEN.show(fb), the code has to:
- check the fb widtrh, height, format and accordingly will process the bytearray to tranfer the equivalent of a 160x128x2 array.
1. if the Framebuffer is 160x128 in RGB565 mode, nothing to do, DMA powered SPI transfer.
2. if not, pixel per pixel, the byterarray will be converted to a RGB565 pixel and transfered thru the SPI interface.
Now the implementation
- the format, width, height are stored in the mp_obj_framebuf_t struct and I need them in show(fb) to know what the bytearray is (ref: http://meowbit-doc.kittenbot.cn/#/micro ... E%E7%A4%BA
- the current code uses this snippet to get the bytearray:
Code: Select all
mp_get_buffer_raise(args, &bufinfo, MP_BUFFER_READ);
byte *p = bufinfo.buf;
- as the struct mp_obj_framebuf_t and FRAMEBUF_* are defined in modframebuf.c, there are not public so this code does not compile:
Code: Select all
mp_obj_framebuf_t *fb = MP_OBJ_TO_PTR(args);
uint8_t format = fb->format;
As a result my questions
- are my assumptions right or wrong ?
- is there a better way to do ?
- if not, why mp_obj_framebuf_t and defines are not exposed in a .h file ? Is there a good reason ? Else I will create it as you suggested.
8bits should be enough...