[Graphics] [pokeemerald] Team preview in overworld

[LycosIUT]

I'm trying to create a gym leader preview on the signs in front of the gym itself.

So far I achieved to display the trainer and all the team :

Spoiler:

Now I would like to add a black background window with a bit of transparency, exactly what is already done one starter selection for the pokémon label :

Spoiler:

Here i'm totally lost and i can't get something to work properly. I just can't figure out how windows are managed exactly and i think the problem might be palette related.
The window either don't show up or does not have the right color and transparency.

Here is my code so far :

Spoiler:

src/script_menu.c

static const struct WindowTemplate sWindowTemplate_TrainerTeamWindow =
{
    .bg = 0,
    .tilemapLeft = 0,
    .tilemapTop = 0,
    .width = 13,
    .height = 4,
    .paletteNum = 14,
    .baseBlock = 0x0274
};

static const u8 sTextColors[] = {TEXT_COLOR_TRANSPARENT, TEXT_COLOR_WHITE, TEXT_COLOR_LIGHT_GRAY};

static const s16 sPreviewTeamLocation[PARTY_SIZE][2] =
{
    {56,     30},
    {184,    30},
    {200,    80},
    {40,     80},
    {56,     130},
    {184,    130}
};

#define tState    data[0]
#define tWindowId data[1]
#define tSpriteNumber data[2]
#define tTrainerSpriteId data[3]
#define tMonSpriteId(i)     data[i + 4]

bool8 ScriptMenu_ShowTrainerTeam(u16 trainerId)
{
    if (FindTaskIdByFunc(Task_DisplayTrainerTeam) != TASK_NONE)
    {
        return FALSE;
    }
    else
    {
        u8 taskId;
        u8 windowId;
        u8 i;
        u8 width;
        const struct Trainer *trainer = &gTrainers[trainerId];
        struct WindowTemplate winTemplate;
        taskId = CreateTask(Task_DisplayTrainerTeam, 80);

        // Background window
        winTemplate = sWindowTemplate_TrainerTeamWindow;
        windowId = AddWindow(&winTemplate);
        gTasks[taskId].tWindowId = windowId;
        FillWindowPixelBuffer(windowId, PIXEL_FILL(0));

        width = GetStringCenterAlignXOffset(FONT_NARROW, trainer->trainerName, 0x68);
        AddTextPrinterParameterized3(windowId, FONT_NARROW, width + 20, 30, sTextColors, 0, trainer->trainerName);

        // Display trainer and party sprites
        gTasks[taskId].tTrainerSpriteId = CreateTrainerPicSprite(trainer->trainerPic, TRUE, 120, 80, 12, TAG_NONE);
        gTasks[taskId].tSpriteNumber = trainer->partySize;
        for(i = 0; i < trainer->partySize; i++) {
            u8 startX = sPreviewTeamLocation[i][0];
            u8 startY = sPreviewTeamLocation[i][1];
            u8 spriteId = CreateMonSprite_PicBox(trainer->party.NoItemDefaultMoves[i].species, startX, startY, 0);
            gSprites[spriteId].callback = SpriteCallbackDummy;
            gSprites[spriteId].oam.priority = 0;
            gTasks[taskId].tMonSpriteId(i) = spriteId;
        }
        PutWindowTilemap(windowId);
        //ScheduleBgCopyTilemapToVram(0);
        CopyWindowToVram(windowId, COPYWIN_FULL);

        return TRUE;
    }
}

static void Task_DisplayTrainerTeam(u8 taskId)
{
    s8 selection;
    s16 *data = gTasks[taskId].data;
    u8 i;


    struct Task *task = &gTasks[taskId];

    switch (task->tState)
    {
        case 0:
            task->tState++;
            break;
        case 1:
            //selection = Menu_ProcessInput();
            if (JOY_NEW(A_BUTTON | B_BUTTON))
            {
                task->tState++;
            }
            break;
        case 2:
            for(i = 0; i < task->tSpriteNumber; i++) {
                FreeResourcesAndDestroySprite(&gSprites[task->tMonSpriteId(i)], task->tMonSpriteId(i));
            }
            FreeResourcesAndDestroySprite(&gSprites[task->tTrainerSpriteId], task->tTrainerSpriteId);
            task->tState++;
            break;
        case 3:
            FillWindowPixelBuffer(0, PIXEL_FILL(0));
            ClearWindowTilemap(task->tWindowId);
            RemoveWindow(task->tWindowId);
            task->tWindowId = WINDOW_NONE;
            DestroyTask(taskId);
            ScriptContext_Enable();
            break;
    }
}