fix(esp32): gate RGB LCD driver to ESP32-S3 and add port helpers

Skip rgb_lcd_display_driver on non-S3 targets so AtomVM esp32 CI builds
pass without esp_lcd_panel_rgb.h. Add boot framebuffer fill, measure_text
port command, and document measure_text in display-drivers.md.

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

Author: drlinux

CMakeLists.txt

@@ -20,7 +20,7 @@
 
 # WHOLE_ARCHIVE option is supported only with esp-idf 5.x
 # A link option will be used with esp-idf 4.x
-if (IDF_VERSION_MAJOR GREATER_EQUAL 5)
+if (IDF_VERSION_MAJOR GREATER_EQUAL 5 AND IDF_TARGET STREQUAL "esp32s3")
     set(OPTIONAL_WHOLE_ARCHIVE WHOLE_ARCHIVE)
     set(OPTIONAL_ESP_LCD_REQUIRES "esp_lcd")
     set(OPTIONAL_RGB_LCD_SRCS "rgb_lcd_display_driver.c")

display_driver.c

@@ -20,6 +20,8 @@
 
 #include <stdlib.h>
 
+#include <sdkconfig.h>
+
 #include <esp_idf_version.h>
 #include <esp_log.h>
 
@@ -34,7 +36,7 @@ Context *epaper_display_create_port(GlobalContext *global, term opts);
 Context *dcs_lcd_display_create_port(GlobalContext *global, term opts);
 Context *memory_lcd_display_create_port(GlobalContext *global, term opts);
 Context *oled_display_create_port(GlobalContext *global, term opts);
-#if ESP_IDF_VERSION >= ESP_IDF_VERSION_VAL(5, 0, 0)
+#if ESP_IDF_VERSION >= ESP_IDF_VERSION_VAL(5, 0, 0) && CONFIG_IDF_TARGET_ESP32S3
 Context *rgb_lcd_display_create_port(GlobalContext *global, term opts);
 #endif
 
@@ -58,7 +60,7 @@ Context *display_create_port(GlobalContext *global, term opts)
     if (!strcmp(compat_string, "waveshare,5in65-acep-7c")
         || !strcmp(compat_string, "good-display/gdep073e01")) {
         ctx = epaper_display_create_port(global, opts);
-#if ESP_IDF_VERSION >= ESP_IDF_VERSION_VAL(5, 0, 0)
+#if ESP_IDF_VERSION >= ESP_IDF_VERSION_VAL(5, 0, 0) && CONFIG_IDF_TARGET_ESP32S3
     } else if (!strcmp(compat_string, "waveshare,esp32-s3-touch-lcd-7")
         || !strcmp(compat_string, "esp_lcd,rgb")) {
         ctx = rgb_lcd_display_create_port(global, opts);

display_task.c

@@ -144,6 +144,72 @@ static bool try_handle_register_font(Message *message, Context *ctx)
     return true;
 }
 
+static bool try_handle_measure_text(Message *message, Context *ctx)
+{
+    GenMessage gen_message;
+    if (UNLIKELY(port_parse_gen_message(message->message,
+                &gen_message) != GenCallMessage)) {
+        return false;
+    }
+
+    term req = gen_message.req;
+    if (UNLIKELY(!term_is_tuple(req) || term_get_tuple_arity(req) < 3)) {
+        return false;
+    }
+    term cmd = term_get_tuple_element(req, 0);
+
+    if (cmd != globalcontext_make_atom(ctx->global,
+                "\xC" "measure_text")) {
+        return false;
+    }
+
+    char *handle = interop_atom_to_string(ctx,
+            term_get_tuple_element(req, 1));
+    EpdFont *loaded_font = NULL;
+    if (handle != NULL) {
+        loaded_font = ufont_manager_find_by_handle(ufont_manager, handle);
+        free(handle);
+    }
+
+    term text_bin = term_get_tuple_element(req, 2);
+    size_t text_len = term_binary_size(text_bin);
+    char *text = malloc(text_len + 1);
+    if (text == NULL) {
+        BEGIN_WITH_STACK_HEAP(TUPLE_SIZE(2) + REF_SIZE, heap);
+        term return_tuple = term_alloc_tuple(2, &heap);
+        term_put_tuple_element(return_tuple, 0, gen_message.ref);
+        term_put_tuple_element(return_tuple, 1, ERROR_ATOM);
+        display_message_send(gen_message.pid, return_tuple, ctx->global);
+        END_WITH_STACK_HEAP(heap, ctx->global);
+        return true;
+    }
+    memcpy(text, term_binary_data(text_bin), text_len);
+    text[text_len] = '\0';
+
+    int width = 0;
+    int height = 0;
+    if (loaded_font != NULL) {
+        EpdFontProperties props = epd_font_properties_default();
+        EpdRect rect = epd_get_string_rect(loaded_font, text, 0, 0, 0, &props);
+        width = rect.width;
+        height = rect.height;
+    }
+    free(text);
+
+    BEGIN_WITH_STACK_HEAP(TUPLE_SIZE(3) + TUPLE_SIZE(2) + REF_SIZE, heap);
+    term result = term_alloc_tuple(3, &heap);
+    term_put_tuple_element(result, 0, OK_ATOM);
+    term_put_tuple_element(result, 1, term_from_int(width));
+    term_put_tuple_element(result, 2, term_from_int(height));
+    term return_tuple = term_alloc_tuple(2, &heap);
+    term_put_tuple_element(return_tuple, 0, gen_message.ref);
+    term_put_tuple_element(return_tuple, 1, result);
+    display_message_send(gen_message.pid, return_tuple, ctx->global);
+    END_WITH_STACK_HEAP(heap, ctx->global);
+
+    return true;
+}
+
 void display_task_process_messages(void *arg)
 {
     struct DisplayTaskArgs *args = arg;
@@ -154,7 +220,8 @@ void display_task_process_messages(void *arg)
         Message *message;
         xQueueReceive(args->messages_queue, &message, portMAX_DELAY);
 
-        if (!try_handle_register_font(message, args->ctx)) {
+        if (!try_handle_register_font(message, args->ctx)
+                && !try_handle_measure_text(message, args->ctx)) {
             args->process_message_fn(message, args->ctx);
         }
 

docs/display-drivers.md

@@ -395,6 +395,16 @@ like progress bars or dynamic text fields where a full-screen redraw is unnecess
 :port.call(display, {:update_region, x, y, width, height, display_list}, 500)
 ```
 
+### measure_text
+
+Returns the pixel width and height of a text string for a registered uFont handle.
+Use this to size marquee regions or layout before building a display list.
+
+```elixir
+# {:ok, width, height} or {:error, reason}
+:port.call(display, {:measure_text, :default16px, "Hello"}, 500)
+```
+
 ### draw_buffer
 
 Draws a preformatted RGB565 buffer already resident in memory. Each pixel is 2 bytes

rgb_lcd_display_driver.c

@@ -49,6 +49,9 @@
 
 static const char *TAG = "rgb_lcd_display_driver";
 
+/* Matches display_server COLOR_BG (16#1A1A); solid fill before first scanout. */
+#define RGB565_BOOT_FILL_BYTE 0x1A
+
 struct RGBLCDDriver
 {
     esp_lcd_panel_handle_t panel;
@@ -1037,10 +1040,13 @@ static void display_init(Context *ctx, term opts)
     void *fb1 = NULL;
     err = esp_lcd_rgb_panel_get_frame_buffer(driver->panel, 2, &fb0, &fb1);
     if (err == ESP_OK && fb0 && fb1) {
+        size_t fb_bytes = (size_t) width * (size_t) height * sizeof(uint16_t);
+        memset(fb0, RGB565_BOOT_FILL_BYTE, fb_bytes);
+        memset(fb1, RGB565_BOOT_FILL_BYTE, fb_bytes);
         driver->framebuffers[0] = fb0;
         driver->framebuffers[1] = fb1;
         driver->framebuffer_count = 2;
-        ESP_LOGI(TAG, "Using RGB LCD double framebuffer: %p %p", fb0, fb1);
+        ESP_LOGI(TAG, "Using RGB LCD double framebuffer: %p %p (boot fill)", fb0, fb1);
     } else {
         ESP_LOGW(TAG, "RGB LCD multi-framebuffer unavailable, using draw_bitmap path: %s", esp_err_to_name(err));
     }