- code examples : 

This is example code "Hello World" with back button using flipper build tool.

flipper build tool doc : https://github.com/flipperdevices/flipperzero-firmware/blob/dev/documentation/fbt.md

hello_world.c : 

#include <furi.h>
#include <gui/gui.h>
#include <stdlib.h>
#include <gui/elements.h>
#include <input/input.h>

static void render_callback(Canvas* const canvas, void* ctx) {


    (void)ctx;
    // Clear the canvas
    canvas_clear(canvas);

    // Set font
    canvas_set_font(canvas, FontPrimary);

    // Draw the text
    elements_multiline_text_aligned(canvas, 64, 32, AlignCenter, AlignTop, "Hello World");
}

// Input callback function
static void input_callback(InputEvent* input_event, void* ctx) {
    bool* running = (bool*)ctx;

    if(input_event->type == InputTypeShort) {
        if(input_event->key == InputKeyBack) {
            *running = false;
        }
    }
}

int32_t hello_world_app(void) {
    // Create and open a viewport
    ViewPort* view_port = view_port_alloc();
    view_port_draw_callback_set(view_port, render_callback, NULL);
    Gui* gui = furi_record_open(RECORD_GUI);
    gui_add_view_port(gui, view_port, GuiLayerFullscreen);

    // Create an input queue
    FuriMessageQueue* input_queue = furi_message_queue_alloc(8, sizeof(InputEvent));

    // Main loop control variable
    bool running = true;

    // Register input callback
    view_port_input_callback_set(view_port, input_callback, &running);

    // Main loop
    while(running) {
        view_port_update(view_port);
        furi_delay_ms(100);

        // Check for input events
        InputEvent input_event;
        while(furi_message_queue_get(input_queue, &input_event, 0) == FuriStatusOk) {
            input_callback(&input_event, &running);
        }
    }

    // Cleanup
    view_port_enabled_set(view_port, false);
    gui_remove_view_port(gui, view_port);
    furi_record_close(RECORD_GUI);
    view_port_free(view_port);
    furi_message_queue_free(input_queue);

    return 0;
}


- errors : 

error 1 :
error: unused parameter 'ctx' [-Werror=unused-parameter]
    7 | static void render_callback(Canvas* const canvas, void* ctx) {
      |                                                   ~~~~~~^~~
cc1-bin: all warnings being treated as errors
        SDKCHK  targets/f7/api_symbols.csv
scons: *** [build/f7-firmware-D/.extapps/hello_world/testingapp.o] Error 1

solve 1 : 

using (void)ctx; in functions if not used.