fix(rgb_lcd): device-proven compositor, uFont color, and draw_buffer

Blend transparent RGBA pixels over restored background with optional
lower-layer resolve instead of stalling on alpha==0. Restore
RRGGBBAA uFont fgcolor layout. Accept draw_buffer binary tuples and
persist partial cover draws into background_buffer.

Signed-off-by: Ibrahim YILMAZ <ibrahim@drlinux.org>
Co-authored-by: Cursor <cursoragent@cursor.com>

Author: drlinux

dcs_lcd_draw.c

@@ -249,12 +249,13 @@ int dcs_lcd_draw_image_x(const struct DCSLCDScreen *screen,
             pixmem16[drawn_pixels] = rgb565_color_to_surface(blended);
         } else if (alpha > 0) {
             uint16_t color = rgba8888_color_to_rgb565(img_pixel);
-            uint16_t lower = 0;
-            (void) dcs_lcd_resolve_pixel_rgb565(screen, xpos + drawn_pixels, ypos, items, items_len, item_index + 1, &lower);
+            uint16_t lower = rgb565_color_to_surface(pixmem16[drawn_pixels]);
+            uint16_t resolved = 0;
+            if (dcs_lcd_resolve_pixel_rgb565(screen, xpos + drawn_pixels, ypos, items, items_len, item_index + 1, &resolved)) {
+                lower = resolved;
+            }
             uint16_t blended = alpha_blend_rgb565(color, lower, alpha);
             pixmem16[drawn_pixels] = rgb565_color_to_surface(blended);
-        } else {
-            return drawn_pixels;
         }
         drawn_pixels++;
         pixels++;
@@ -427,12 +428,13 @@ int dcs_lcd_draw_scaled_cropped_img_x(const struct DCSLCDScreen *screen,
             pixmem16[drawn_pixels] = rgb565_color_to_surface(blended);
         } else if (alpha > 0) {
             uint16_t color = rgba8888_color_to_rgb565(img_pixel);
-            uint16_t lower = 0;
-            (void) dcs_lcd_resolve_pixel_rgb565(screen, xpos + drawn_pixels, ypos, items, items_len, item_index + 1, &lower);
+            uint16_t lower = rgb565_color_to_surface(pixmem16[drawn_pixels]);
+            uint16_t resolved = 0;
+            if (dcs_lcd_resolve_pixel_rgb565(screen, xpos + drawn_pixels, ypos, items, items_len, item_index + 1, &resolved)) {
+                lower = resolved;
+            }
             uint16_t blended = alpha_blend_rgb565(color, lower, alpha);
             pixmem16[drawn_pixels] = rgb565_color_to_surface(blended);
-        } else {
-            return drawn_pixels;
         }
         drawn_pixels++;
         int next_rel_x = j + 1;

display_items.c

@@ -36,8 +36,7 @@ struct Surface
     int width;
     int height;
     void *buffer;
-    uint32_t fg_color; // RGB bytes in 0x00BBGGRR order; alpha is cleared
-                       // so epd_draw_pixel can append per-pixel alpha.
+    uint32_t fg_color; // 0xRRGGBBAA from Erlang color << 8 | 0xFF
 };
 
 #define BPP 4
@@ -60,9 +59,9 @@ void epd_draw_pixel(int xpos, int ypos, uint8_t color, void *buffer)
     // the foreground RGB on transparent with anti-aliased alpha
     // derived from the inverted grayscale.
     uint8_t alpha = (15 - (color >> 4)) * 17;
-    pixel[0] = surface->fg_color & 0xFFu;
-    pixel[1] = (surface->fg_color >> 8) & 0xFFu;
-    pixel[2] = (surface->fg_color >> 16) & 0xFFu;
+    pixel[0] = (surface->fg_color >> 24) & 0xFFu;
+    pixel[1] = (surface->fg_color >> 16) & 0xFFu;
+    pixel[2] = (surface->fg_color >> 8) & 0xFFu;
     pixel[3] = alpha;
 }
 #endif /* ENABLE_UFONT */
@@ -97,8 +96,8 @@ static bool parse_image_tuple(term img, Context *ctx, int *width, int *height, c
 
     size_t expected = (size_t) *width * (size_t) *height * bytes_per_pixel;
     if (term_binary_size(data_term) < expected) {
-        fprintf(stderr, "image binary too small (%zu < %zu)\n",
-            term_binary_size(data_term), expected);
+        fprintf(stderr, "image binary too small (%lu < %zu)\n",
+            (unsigned long) term_binary_size(data_term), expected);
         return false;
     }
 
@@ -272,12 +271,7 @@ void display_items_init_item(BaseDisplayItem *item, term req, Context *ctx)
                 return;
             }
             memset(surface.buffer, 0, surface_bytes);
-            // Convert Erlang fgcolor (0xRRGGBBAA) to RGBA8888 little-
-            // endian byte order (R in low byte, alpha byte cleared) so
-            // epd_draw_pixel can OR it with the per-pixel alpha.
-            surface.fg_color = ((fgcolor >> 24) & 0xFFu)
-                    | (((fgcolor >> 16) & 0xFFu) << 8)
-                    | (((fgcolor >> 8) & 0xFFu) << 16);
+            surface.fg_color = fgcolor;
             int text_x = 0;
             int text_y = loaded_font->ascender;
             enum EpdDrawError res = epd_write_default(loaded_font, text, &text_x, &text_y, &surface);

rgb_lcd_display_driver.c

@@ -753,6 +753,24 @@ static void do_draw_rgb565_rle_base64(Context *ctx, int x, int y, int width, int
     do_draw_rgb565_rle_base64_scaled(ctx, x, y, width, height, width, height, b64_term);
 }
 
+static void maybe_store_cover_background(
+    struct RGBLCDDriver *driver, int x, int y, int width, int height, const uint16_t *pixels)
+{
+    if (!driver->background_buffer || x < 0 || y < 0 || width <= 0 || height <= 0) {
+        return;
+    }
+    if (x + width > driver->screen.w || y + height > driver->screen.h) {
+        return;
+    }
+
+    for (int row = 0; row < height; row++) {
+        memcpy(
+            driver->background_buffer + ((size_t) (y + row) * driver->screen.w) + x,
+            pixels + ((size_t) row * width),
+            (size_t) width * sizeof(uint16_t));
+    }
+}
+
 static void draw_rgb565_region(struct RGBLCDDriver *driver, int x, int y, int width, int height, const uint16_t *pixels)
 {
     if (driver->framebuffer_count > 1) {
@@ -785,6 +803,7 @@ static void draw_rgb565_region(struct RGBLCDDriver *driver, int x, int y, int wi
         mirror_region_to_inactive_framebuffers(driver, x, y, width, height, pixels);
     }
 
+    maybe_store_cover_background(driver, x, y, width, height, pixels);
     ESP_LOGI(TAG, "draw_rgb565_region: %dx%d pixels at (%d,%d)", width, height, x, y);
 }
 
@@ -840,14 +859,31 @@ static void process_message(Message *message, Context *ctx)
         int y = term_to_int(term_get_tuple_element(req, 2));
         int width = term_to_int(term_get_tuple_element(req, 3));
         int height = term_to_int(term_get_tuple_element(req, 4));
-        unsigned long addr_low = term_to_int(term_get_tuple_element(req, 5));
-        unsigned long addr_high = term_to_int(term_get_tuple_element(req, 6));
-        const uint16_t *data = (const uint16_t *) (addr_low | (addr_high << 16));
-
-        if (!data || width <= 0 || height <= 0 || x < 0 || y < 0
-                || x + width > driver->screen.w || y + height > driver->screen.h) {
-            ESP_LOGE(TAG, "Invalid draw_buffer arguments.");
-            return;
+        term payload = term_get_tuple_element(req, 5);
+        const uint16_t *data = NULL;
+
+        if (term_is_binary(payload)) {
+            size_t expected = (size_t) width * (size_t) height * 2;
+            if (width <= 0 || height <= 0 || x < 0 || y < 0
+                    || x + width > driver->screen.w || y + height > driver->screen.h
+                    || term_binary_size(payload) < expected) {
+                ESP_LOGE(TAG, "Invalid draw_buffer binary arguments.");
+                return;
+            }
+            data = (const uint16_t *) term_binary_data(payload);
+        } else {
+            if (term_get_tuple_arity(req) < 7) {
+                ESP_LOGE(TAG, "Invalid draw_buffer pointer arguments.");
+                return;
+            }
+            unsigned long addr_low = term_to_int(payload);
+            unsigned long addr_high = term_to_int(term_get_tuple_element(req, 6));
+            data = (const uint16_t *) (addr_low | (addr_high << 16));
+            if (!data || width <= 0 || height <= 0 || x < 0 || y < 0
+                    || x + width > driver->screen.w || y + height > driver->screen.h) {
+                ESP_LOGE(TAG, "Invalid draw_buffer pointer arguments.");
+                return;
+            }
         }
 
         draw_rgb565_region(driver, x, y, width, height, data);