Add support for 18 bit SPI graphics (ILI9488)

src/nanoFramework.Graphics/Graphics/Displays/DisplayInterface.h

@@ -1,4 +1,4 @@
-//
+//
 // Copyright (c) .NET Foundation and Contributors
 // See LICENSE file in the project root for full license information.
 //
@@ -88,6 +88,13 @@ struct DisplayInterface
         CLR_UINT32 height,
         CLR_UINT32 stride,
         bool doByteSwap);
+    void SendData18Windowed(
+        CLR_UINT16 *data,
+        CLR_UINT32 startX,
+        CLR_UINT32 startY,
+        CLR_UINT32 width,
+        CLR_UINT32 height,
+        CLR_UINT32 stride);
     void FillData16(CLR_UINT16 fillValue, CLR_UINT32 fillLength);
     void SetCommandMode(int mode);
 };

src/nanoFramework.Graphics/Graphics/Displays/Generic_SPI.cpp

@@ -1,4 +1,4 @@
-//
+//
 // Copyright (c) .NET Foundation and Contributors
 // Portions Copyright (c) Microsoft Corporation.  All rights reserved.
 // See LICENSE file in the project root for full license information.
@@ -260,7 +260,16 @@ void DisplayDriver::Clear()
 
         g_DisplayInterface.SendCommand(1, g_DisplayInterfaceConfig.GenericDriverCommands.MemoryWrite);
 
-        g_DisplayInterface.FillData16(0, Attributes.Width * Attributes.Height);
+        if (Attributes.BitsPerPixel <= 16)
+        {
+            // 2 bytes per pixel
+            g_DisplayInterface.FillData16(0, Attributes.Width * Attributes.Height);
+        }
+        else
+        {
+            // 3 bytes per pixel
+            g_DisplayInterface.FillData16(0, (Attributes.Width * Attributes.Height * 3 + 1) / 2);
+        }
     }
     else
     {
@@ -289,16 +298,23 @@ void DisplayDriver::BitBlt(
     int screenY,
     CLR_UINT32 data[])
 {
-    // 16 bit colour  RRRRRGGGGGGBBBBB mode 565
-
     ASSERT((screenX >= 0) && ((screenX + width) <= Attributes.Width));
     ASSERT((screenY >= 0) && ((screenY + height) <= Attributes.Height));
 
     SetWindow(screenX, screenY, (screenX + width - 1), (screenY + height - 1));
 
     g_DisplayInterface.SendCommand(1, g_DisplayInterfaceConfig.GenericDriverCommands.MemoryWrite);
 
-    g_DisplayInterface.SendData16Windowed((CLR_UINT16 *)&data[0], srcX, srcY, width, height, stride, true);
+    if (Attributes.BitsPerPixel <= 16)
+    {
+        // 16-bit / two byte pixel formats. RGB mode 565
+        g_DisplayInterface.SendData16Windowed((CLR_UINT16 *)&data[0], srcX, srcY, width, height, stride, true);
+    }
+    else
+    {
+        // 18-bit / three byte pixel formats. RGB mode 666
+        g_DisplayInterface.SendData18Windowed((CLR_UINT16 *)&data[0], srcX, srcY, width, height, stride);
+    }
 
     return;
 }

src/nanoFramework.Graphics/Graphics/Displays/Spi_To_Display.cpp

@@ -1,4 +1,4 @@
-//
+//
 // Copyright (c) .NET Foundation and Contributors
 // See LICENSE file in the project root for full license information.
 //
@@ -307,6 +307,65 @@ void DisplayInterface::SendData16Windowed(
     return;
 }
 
+void DisplayInterface::SendData18Windowed(
+    CLR_UINT16 *data,
+    CLR_UINT32 startX,
+    CLR_UINT32 startY,
+    CLR_UINT32 width,
+    CLR_UINT32 height,
+    CLR_UINT32 stride)
+{
+    // Offset for window start
+    CLR_UINT16 *startOfLine = data + (startY * stride) + startX;
+
+    CLR_UINT8 *byteBuffer = (CLR_UINT8 *)currentBuffer;
+    CLR_UINT32 bytesWritten = 0;
+
+    while (height--)
+    {
+        CLR_UINT16 *pixel = startOfLine;
+
+        for (CLR_UINT32 x = 0; x < width; x++)
+        {
+            CLR_UINT16 color = *pixel++;
+
+            // Extract RGB565 components and bit-widen to 8-bit
+            CLR_UINT8 b = color & 0x1F;
+            CLR_UINT8 g = (color >> 5) & 0x3F;
+            CLR_UINT8 r = (color >> 11) & 0x1F;
+
+            b = (b << 3) | (b >> 2);
+            g = (g << 2) | (g >> 4);
+            r = (r << 3) | (r >> 2);
+
+            // Ensure there is room for a full pixel
+            if (bytesWritten + 3 > SPI_MAX_TRANSFER_SIZE)
+            {
+                InternalSendBytes((CLR_UINT8 *)currentBuffer, bytesWritten, true);
+                SwapBuffers();
+                byteBuffer = (CLR_UINT8 *)currentBuffer;
+                bytesWritten = 0;
+            }
+
+            byteBuffer[bytesWritten++] = b;
+            byteBuffer[bytesWritten++] = g;
+            byteBuffer[bytesWritten++] = r;
+        }
+
+        startOfLine += stride;
+    }
+
+    // Flush remaining bytes
+    if (bytesWritten > 0)
+    {
+        InternalSendBytes((CLR_UINT8 *)currentBuffer, bytesWritten, true);
+
+        SwapBuffers();
+    }
+
+    return;
+}
+
 void DisplayInterface::FillData16(CLR_UINT16 fillValue, CLR_UINT32 fillLength)
 {
     // Fill the current buffer full of fillValue, or as much as we need