Adding SPI Lcd to work under 2DGraphics and more

[u77345]

How do I add an SPI LCD to be used with 2DGraphics and potentially as ScreenDevice and CharDevice?
I started an implementation at https://github.com/u77345/circle/blob/master/addon/display/ili9341.cpp

[dlbogdan]

Coincidentally, I’m building a generic driver class + an implementation for an SSD1322 oled display to go with it. I am tailoring it to go with lvgl addon though. We should talk and add your LCD as well to the mix.

[u77345]

LVGL makes sense. I see samples/lvgl uses circle's CScreenDevice. Happy to collaborate.

[dlbogdan]

Only the Circle lib provided wrapper class CLVGL uses 2DGraphics, not lvgl itself. Initially I wanted to go the same route but there is a lot to modify in 2DGraphics class because it’s tailored with RGB 16/32bpp displays on DSI/HDMI in mind, with hardware framebuffer. My OLED for example is a 4bpp grayscale display. It’s a lot easier to build my own generic driver class for I2C/SPI and the OLED driver itself as well as others that come in my hand, and then in the same files create another wrapper class for LVGL. Also the project I’m working on will not have any pointing devices at all, as the inputs will be from rotary encoders and buttons. CLVGL wrapper class expects on having a mouse or a touchscreen, which is fine for a lot of cases but not all of them as you may see.

[u77345]

I have identical requirements - to fit ILI9341 into MiniDexed, on board with your approach.

[dlbogdan]

Great. As soon as I finish my classes and test a bit, I’ll share my generic driver class as well as the lvgl wrapper so you can test with your display. I’m aiming to make the lvgl wrapper it a seemless swap with CLVGL, compatible so existing apps such as minidexed should only initialize the display hardware by the use of its driver constructor and use it with no other modifications.

[dlbogdan]

https://youtube.com/shorts/eMTahYKymk0?feature=share

It works!
what’s left:

• clean up the hardcoding to make it truly generic
• optimize a bit (maybe DMA transfers, we’ll see)
• Another class for encoders and gpio buttons as inputs

what you should have ready in the meantime:
A putpixel function that uses an internal framebuffer
A flush function that writes the framebuffer to the screen
A init function that initializes the display.
optionally: a blitter function that converts and copies a lv_color_t * frambuffer (32bpp for ex) to your native framebuffer format.
if you use dma, you also need a function that gets called when the transfer finishes.

Regards.

[rsta2]

How do I add an SPI LCD to be used with 2DGraphics and potentially as ScreenDevice and CharDevice?

Unfortunately this is currently not supported. I think, this shouldn't be included directly in CScreenDevice and C2DGraphics. There should be separate classes for SPI LCD displays in addon/display for this purpose and it should be possible to extend this for other SPI displays in the future. For LVGL I think, there should also a specific class (e.g. CLGVL_SPI). I wouldn't mix SPI support with the frame buffer. Where it makes sense, a generic base class could be used. I'm open for suggestions.

[dlbogdan]

Hi Rene,
First of all, thank you immensely for your work. I can’t really be thankful enough for Circle.
Now, I have a personal project in my hands and am taking the opportunity to build two new generic driver classes for LVGL/Circle:
One, a wrapper class CGLVGL for the lvgl graphics, to interface with various spi/i2c screens of various depth and resolutions.
And a second one CILVGL for the lvgl input handling , customizable with rotary encoders and buttons attached to GPIOs on the raspberry pi.
Even though I lack time, as I have two small kids, I’m confident that I can have something production ready in about a week or two.

Best to you!

[rsta2]

Thank you! I'm looking forward to your contribution.

[dlbogdan]

Short update:
Got a lot of things working smoothly, some aren’t yet done, as I’ve had a terribly busy week at work. Had to remake the rotary encoder on my own implementation as the one included in circle/addon/sensor wouldn’t work at all, at least on raspberry pi zero.

Anyway, here’s a video. Two types of input devices: 4 buttons in corners (on GPIOs) and a rotary encoder.
The menu you’re seeing in the video is part of a bigger project, which I will make open source when done, as well as all the classes, drivers for displays and inputs that I needed to do.

https://youtu.be/a7K2PldYtTE

[rsta2]

Looks good! Take the time, you need. There's no hurry.

[u77345]

@dlbogdan Would you be open to collaborate on the driver?