How to use text in EFI graphic mode? - c

Question

I am super new to creating efi application. My aim is to create a small application in efi, that displays some text on a background. But I am stuck with trying to display text on the display (Great would be to have a custom font, but that is not necessary at this stage). I want the app (also) to run on apple systems (to boot from a usb)
How do I find good documentation on the EFI functions? It seems super hard to find good examples etc.
How can I display a text on a background with EFI?
This is what I got so far. I change the background to a color using the graphics protocol. How do I display a text on it. The Output String doesn't seem to work.
#include "efibind.h"
#include "efidef.h"
#include "efidevp.h"
#include "eficon.h"
#include "efiapi.h"
#include "efierr.h"
#include "efiprot.h"
static EFI_GUID GraphicsOutputProtocolGUID = EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID;
/**
* efi_main - The entry point for the EFI application
* #image: firmware-allocated handle that identifies the image
* #SystemTable: EFI system table
*/
EFI_STATUS efi_main(EFI_HANDLE image, EFI_SYSTEM_TABLE *systemTable) {
EFI_BOOT_SERVICES *bs = systemTable->BootServices;
EFI_STATUS status;
EFI_GRAPHICS_OUTPUT_PROTOCOL *graphicsProtocol;
SIMPLE_TEXT_OUTPUT_INTERFACE *conOut = systemTable->ConOut;
EFI_GRAPHICS_OUTPUT_MODE_INFORMATION *info;
UINTN SizeOfInfo, sWidth, sHeight;
status = bs->LocateProtocol(&GraphicsOutputProtocolGUID, NULL,
(void**)&graphicsProtocol);
if (EFI_ERROR(status) || graphicsProtocol == NULL) {
conOut->OutputString(conOut, L"Failed to init gfx!\r\n");
return status;
}
conOut->ClearScreen(conOut);
//Switch to current mode so gfx is started.
status = graphicsProtocol->SetMode(graphicsProtocol, graphicsProtocol->Mode->Mode);
if (EFI_ERROR(status)) {
conOut->OutputString(conOut, L"Failed to set default mode!\r\n");
return status;
}
EFI_GRAPHICS_OUTPUT_BLT_PIXEL p;
p.Red = 200;
p.Green = 77;
p.Blue = 13;
graphicsProtocol->QueryMode(graphicsProtocol, graphicsProtocol->Mode->Mode, &SizeOfInfo, &info);
sWidth = info->HorizontalResolution;
sHeight = info->VerticalResolution;
status = graphicsProtocol->Blt(graphicsProtocol, &p, EfiBltVideoFill, 0, 0, 0, 0, sWidth, sHeight, 0);
while (1) {
conOut->OutputString(conOut, L"Some text that I want to display\r\n");
bs->Stall(500000);
}
return EFI_SUCCESS;
}

Answer 1

UEFI supports graphics output. It also supports text output (which can mean either output to a serial console, or text rendered to a graphical console, or both). But there is no defined way to interact between these in a controlled manner.
Applications that provide a graphical environment with text elements (BIOS configuration menu, GRUB) generally do this using their own frameworks to draw text on the graphical console using GRAPHICS_OUTPUT_PROTOCOL.

Answer 2

This is a short example of a text renderer using the font module from LVGL (which can be used standalone, replace #include "../../lv_conf.h" in the lv_font.h file with #define USE_LV_FONT_DEJAVU_20 8) and the Blt method from the GRAPHICS_OUTPUT_PROTOCOL
#include <Uefi.h>
#include <Library\UefiLib.h>
#include <Protocol\GraphicsOutput.h>
#include "lv_font.h"
#define LETTER_SPACE 2
#define WAIT_SECONDS 10
#define FONT &lv_font_dejavu_20
static EFI_BOOT_SERVICES *gBS;
static EFI_RUNTIME_SERVICES *gRT;
static EFI_GRAPHICS_OUTPUT_PROTOCOL *gGOP = (EFI_GRAPHICS_OUTPUT_PROTOCOL *)NULL;
static EFI_GRAPHICS_OUTPUT_BLT_PIXEL gWhite = { 255,255,255,0 };
static void _util_render_glyph(UINT32 x, UINT32 y, CHAR8 letter)
{
UINT32 height;
UINT32 width;
UINT32 pm_x;
UINT32 pm_y;
UINT32 index;
const UINT8* bitmap;
EFI_GRAPHICS_OUTPUT_BLT_PIXEL *pixelmap;
if (gGOP == NULL) {
return;
}
height = lv_font_get_height(FONT);
width = lv_font_get_width(FONT, letter);
// glyph is not defined in this font
if (width == 0) {
return;
}
bitmap = lv_font_get_bitmap(FONT, letter);
// using 8 bpp for simplicity
if (EFI_ERROR(gBS->AllocatePool(EfiLoaderData, height * width * sizeof(*pixelmap), (VOID**)&pixelmap))) {
return;
}
gBS->SetMem((VOID*)pixelmap, height * width * sizeof(*pixelmap), 0);
// get the current content of the framebuffer to allow 'transparent' blt operations
gGOP->Blt(gGOP, pixelmap, EfiBltVideoToBltBuffer, x, y, 0, 0, width, height, 0);
for (pm_y = 0; pm_y < height; pm_y++) {
for (pm_x = 0; pm_x < width; pm_x++) {
index = width * pm_y + pm_x;
if (bitmap[index] > 200) {
pixelmap[index].Red = 0;
pixelmap[index].Blue = 0;
pixelmap[index].Green = 0;
pixelmap[index].Reserved = 0;
}
else if (bitmap[index] > 100) {
pixelmap[index].Red = 105;
pixelmap[index].Blue = 105;
pixelmap[index].Green = 105;
pixelmap[index].Reserved = 0;
}
}
}
gGOP->Blt(gGOP, pixelmap, EfiBltBufferToVideo, 0, 0, x, y, width, height, 0);
gBS->FreePool(pixelmap);
}
static void _util_render_text(UINT32 x, UINT32 y, const CHAR8 *string)
{
UINT32 index;
UINTN length;
UINT32 scr_w;
UINT32 scr_h;
UINT32 str_x;
UINT32 gly_w;
UINT32 gly_h;
if (string == NULL) {
return;
}
if (gGOP == NULL) {
return;
}
scr_w = gGOP->Mode->Info->HorizontalResolution;
scr_h = gGOP->Mode->Info->VerticalResolution;
length = AsciiStrnLenS(string, 32);
gly_h = lv_font_get_height(FONT);
// check if the string can be printed
if ((y + gly_h) > scr_h) {
return;
}
if (x > scr_w) {
return;
}
// print the string glyph by glyph
str_x = x;
for (index = 0; index < length; index++) {
// check if the glyph can be printed
gly_w = lv_font_get_width(FONT, string[index]);
if ((str_x + gly_w) > scr_w) {
break;
}
// print the glyph
_util_render_glyph(str_x, y, string[index]);
// calculate the position of the next glyph
str_x += gly_w + LETTER_SPACE;
}
}
static void _util_fill_screen(EFI_GRAPHICS_OUTPUT_BLT_PIXEL *color)
{
if (gGOP == NULL) {
return;
}
gGOP->Blt(gGOP, color, EfiBltVideoFill, 0, 0, 0, 0, gGOP->Mode->Info->HorizontalResolution, gGOP->Mode->Info->VerticalResolution, 0);
}
static void _util_wait(UINT32 seconds)
{
EFI_TIME time;
UINT8 current_second = 255;
UINT32 elapsed_seconds = 0;
//wait for some seconds
while (elapsed_seconds <= WAIT_SECONDS) {
if (!EFI_ERROR(gRT->GetTime(&time, (EFI_TIME_CAPABILITIES*)NULL))) {
if (current_second != time.Second) {
elapsed_seconds++;
current_second = time.Second;
}
}
else {
break;
}
CpuPause();
}
}
EFI_STATUS
EFIAPI
UefiMain(
IN EFI_HANDLE ImageHandle,
IN EFI_SYSTEM_TABLE *SystemTable)
{
EFI_STATUS eRc;
gBS = SystemTable->BootServices;
gRT = SystemTable->RuntimeServices;
eRc = gBS->LocateProtocol(
&gEfiGraphicsOutputProtocolGuid,
NULL,
(VOID**)&gGOP);
if (EFI_ERROR(eRc) || gGOP == NULL) {
return EFI_SUCCESS;
}
_util_fill_screen(&gWhite);
_util_render_text(0, 0, "HELLO WORLD!");
_util_wait(WAIT_SECONDS);
return EFI_SUCCESS;
}
I tested it on a pc and on a mac it runs on both. Using the tools provided by LVGL on their website you can use any font you want.

Answer 3

If you target MacEFI specifically, you'll need an additional protocol call to force the console into text mode, like this.