Draw transparent rectangles

[brbrr]

Hi there. I'm trying to figure out how to draw/fill rectangle with transparency. I can fill opaque rectangles without issues. 
I am using `stm32h750`, 320x240 ILI9341 LCD which supports RGB565 buffers. Below is the code that kinda works, but it generates weird colors. In that code, I'm using DMA2D_M2M_BLEND_FG with RGB565 color and I'm setting alpha for the rectangle in the foreground layer.  How can I make it work? 


```

hdma2d.Instance = DMA2D;

hdma2d.Init.Mode = DMA2D_M2M_BLEND_FG;

hdma2d.Init.ColorMode = DMA2D_OUTPUT_RGB565;

hdma2d.Init.AlphaInverted = DMA2D_REGULAR_ALPHA;

hdma2d.Init.RedBlueSwap = DMA2D_RB_REGULAR;

hdma2d.Init.OutputOffset = screen_width - rect.GetWidth();

// Foreground

hdma2d.LayerCfg[1].AlphaMode = DMA2D_REPLACE_ALPHA;

hdma2d.LayerCfg[1].InputColorMode = DMA2D_INPUT_RGB565;

hdma2d.LayerCfg[1].InputOffset = 0;

hdma2d.LayerCfg[1].InputAlpha = alpha;

hdma2d.LayerCfg[1].RedBlueSwap = DMA2D_RB_REGULAR;

hdma2d.LayerCfg[1].AlphaInverted = DMA2D_REGULAR_ALPHA;

// Background

hdma2d.LayerCfg[0].InputAlpha = 0xff;

hdma2d.LayerCfg[0].AlphaMode = DMA2D_REPLACE_ALPHA;

hdma2d.LayerCfg[0].InputColorMode = DMA2D_INPUT_RGB565;

hdma2d.LayerCfg[0].InputOffset = screen_width - rect.GetWidth();

hdma2d.LayerCfg[0].RedBlueSwap = DMA2D_RB_REGULAR;

hdma2d.LayerCfg[0].AlphaInverted = DMA2D_REGULAR_ALPHA;

HAL_DMA2D_Init(&hdma2d);

HAL_DMA2D_ConfigLayer(&hdma2d, 1);

HAL_DMA2D_ConfigLayer(&hdma2d, 0);

HAL_DMA2D_BlendingStart(&hdma2d,

color,

(uint32_t)(buffer + offset),

(uint32_t)(buffer + offset),

rect.GetWidth(),

rect.GetHeight());
```

[Osman SOYKURT]

Hello @brbrr ,

I have some doubts concerning your configuration. Transparency should be used with ARGB888 color.

Can you check that and tell us if it helps?

[brbrr]

Thanks, I did try to use ARGB8888 for BLEND_FG, but unfortunately, I end up with completely messed up colors. For example:
- white (BG) + green@50alpha I end up with blue color
- gray + green@50alpha I'm getting purple 

Below is the updated configuration I am using (note I am converting RGB565 to ARGB8888):

 

uint32_t clr = RGB565toARGB8888(__builtin_bswap16(color), 0);
hdma2d.Instance = DMA2D;
hdma2d.Init.Mode = DMA2D_M2M_BLEND_FG;
hdma2d.Init.ColorMode = DMA2D_OUTPUT_RGB565;
hdma2d.Init.AlphaInverted = DMA2D_REGULAR_ALPHA;
hdma2d.Init.RedBlueSwap = DMA2D_RB_REGULAR;
hdma2d.Init.OutputOffset = screen_width - rect.GetWidth();
// Foreground
hdma2d.LayerCfg[1].AlphaMode = DMA2D_REPLACE_ALPHA;
hdma2d.LayerCfg[1].InputColorMode = DMA2D_INPUT_ARGB8888;
hdma2d.LayerCfg[1].InputOffset = 0;
hdma2d.LayerCfg[1].InputAlpha = alpha;
hdma2d.LayerCfg[1].RedBlueSwap = DMA2D_RB_REGULAR;
hdma2d.LayerCfg[1].AlphaInverted = DMA2D_REGULAR_ALPHA;

 

 

[Osman SOYKURT]

Hello @brbrr ,

Did you succeed in resolving your issue?

[brbrr]

No, unfortunately.