fix(core): create separate display buffer for gamma correction

So that the screenshots in UI tests are not affected by it.
Also not doing the gamma correction in case of SDL_VIDEODRIVER=dummy.

[no changelog]

core/embed/unix/common.c

@@ -148,14 +148,20 @@ static int SDLCALL emulator_event_filter(void *userdata, SDL_Event *event) {
         case SDLK_p:
           display_save("emu");
           return 0;
+#if defined TREZOR_MODEL_T
+        // Left and right arrows controlling display gamma
+        // Only for TT (in button models, arrows do different things)
         case SDLK_LEFT:
           DISPLAY_GAMMA = fmaxf(0.0f, DISPLAY_GAMMA - 0.05f);
           printf("DISPLAY_GAMMA: %0.2f\n", DISPLAY_GAMMA);
+          display_refresh();
           return 0;
         case SDLK_RIGHT:
           DISPLAY_GAMMA = fminf(8.0f, DISPLAY_GAMMA + 0.05f);
           printf("DISPLAY_GAMMA: %0.2f\n", DISPLAY_GAMMA);
+          display_refresh();
           return 0;
+#endif
       }
       break;
   }

core/embed/unix/display-unix.c

@@ -63,7 +63,11 @@
 
 static SDL_Window *WINDOW;
 static SDL_Renderer *RENDERER;
+// BUFFER_TO_DISPLAY will contain the actual pixels to be displayed,
+// it will be filled from BUFFER by gamma-correcting the pixel colors.
+// Screenshots will be taken with data from BUFFER.
 static SDL_Surface *BUFFER;
+static SDL_Surface *BUFFER_TO_DISPLAY;
 static SDL_Texture *TEXTURE, *BACKGROUND;
 
 static SDL_Surface *PREV_SAVED;
@@ -71,9 +75,14 @@ static SDL_Surface *PREV_SAVED;
 static int DISPLAY_BACKLIGHT = -1;
 static int DISPLAY_ORIENTATION = -1;
 float DISPLAY_GAMMA = 0.55f;
+// Will depend on SDL_VIDEODRIVER env variable
+static bool DO_GAMMA_CORRECTION = true;
 int sdl_display_res_x = DISPLAY_RESX, sdl_display_res_y = DISPLAY_RESY;
 int sdl_touch_offset_x, sdl_touch_offset_y;
 
+// Using RGB565 (16-bit) color format.
+typedef uint16_t pixel_color;
+
 // this is just for compatibility with DMA2D using algorithms
 uint8_t *const DISPLAY_DATA_ADDRESS = 0;
 
@@ -89,45 +98,46 @@ static struct {
   } pos;
 } PIXELWINDOW;
 
-uint16_t gamma_correct(uint16_t c) {
+pixel_color gamma_correct(pixel_color c) {
   // NOTE: 0x1f/31 and 0x3f/63 are maximum values of RGB components
   // given the color is 16-bit (5 bits for R, 6 bits for G, 5 bits for B).
   int r = (c >> 11) & 0x1f;
   int g = (c >> 5) & 0x3f;
   int b = c & 0x1f;
 
-  float fr = r / 31.0;
-  float fg = g / 63.0;
-  float fb = b / 31.0;
-
-  fr = pow(fr, DISPLAY_GAMMA);
-  fg = pow(fg, DISPLAY_GAMMA);
-  fb = pow(fb, DISPLAY_GAMMA);
-
-  r = (int)round(fr * 31.0);
-  g = (int)round(fg * 63.0);
-  b = (int)round(fb * 31.0);
+  r = (int)round(pow(r / 31.0, DISPLAY_GAMMA) * 31.0);
+  g = (int)round(pow(g / 63.0, DISPLAY_GAMMA) * 63.0);
+  b = (int)round(pow(b / 31.0, DISPLAY_GAMMA) * 31.0);
 
   return (r << 11) | (g << 5) | b;
 }
 
-void display_pixeldata(uint16_t c) {
+void gamma_correct_buffer_to_display(void) {
+  // Gamma correct all the pixels in BUFFER_TO_DISPLAY.
+  pixel_color *pixels = (pixel_color *)BUFFER_TO_DISPLAY->pixels;
+  for (int y = 0; y < BUFFER_TO_DISPLAY->h; y++) {
+    for (int x = 0; x < BUFFER_TO_DISPLAY->w; x++) {
+      int index = y * BUFFER_TO_DISPLAY->pitch / 2 + x;
+      pixels[index] = gamma_correct(pixels[index]);
+    }
+  }
+}
+
+void display_pixeldata(pixel_color c) {
 #if defined TREZOR_MODEL_1 || defined TREZOR_MODEL_R
   // set to white if highest bits of all R, G, B values are set to 1
   // bin(10000 100000 10000) = hex(0x8410)
   // otherwise set to black
   c = (c & 0x8410) ? 0xFFFF : 0x0000;
-#elif defined TREZOR_MODEL_T
-  c = gamma_correct(c);
 #endif
   if (!RENDERER) {
     display_init();
   }
   if (PIXELWINDOW.pos.x <= PIXELWINDOW.end.x &&
       PIXELWINDOW.pos.y <= PIXELWINDOW.end.y) {
-    ((uint16_t *)
+    ((pixel_color *)
          BUFFER->pixels)[PIXELWINDOW.pos.x + PIXELWINDOW.pos.y * BUFFER->pitch /
-                                                 sizeof(uint16_t)] = c;
+                                                 sizeof(pixel_color)] = c;
   }
   PIXELWINDOW.pos.x++;
   if (PIXELWINDOW.pos.x > PIXELWINDOW.end.x) {
@@ -145,6 +155,7 @@ void display_init_seq(void) {}
 void display_deinit(void) {
   SDL_FreeSurface(PREV_SAVED);
   SDL_FreeSurface(BUFFER);
+  SDL_FreeSurface(BUFFER_TO_DISPLAY);
   if (BACKGROUND != NULL) {
     SDL_DestroyTexture(BACKGROUND);
   }
@@ -167,6 +178,15 @@ void display_init(void) {
   }
   atexit(display_deinit);
 
+  // Not doing gamma correction for "dummy" SDL driver
+  // (not to slow down device/UI tests)
+  char *sdl_env = getenv("SDL_VIDEODRIVER");
+  if (sdl_env && strcmp(sdl_env, "dummy") == 0) {
+    DO_GAMMA_CORRECTION = false;
+  } else {
+    DO_GAMMA_CORRECTION = true;
+  }
+
   char *window_title = NULL;
   char *window_title_alloc = NULL;
   if (asprintf(&window_title_alloc, "Trezor^emu: %s", profile_name()) > 0) {
@@ -200,6 +220,9 @@ void display_init(void) {
   SDL_RenderClear(RENDERER);
   BUFFER = SDL_CreateRGBSurface(0, MAX_DISPLAY_RESX, MAX_DISPLAY_RESY, 16,
                                 0xF800, 0x07E0, 0x001F, 0x0000);
+  BUFFER_TO_DISPLAY =
+      SDL_CreateRGBSurface(0, MAX_DISPLAY_RESX, MAX_DISPLAY_RESY, 16, 0xF800,
+                           0x07E0, 0x001F, 0x0000);
   TEXTURE = SDL_CreateTexture(RENDERER, SDL_PIXELFORMAT_RGB565,
                               SDL_TEXTUREACCESS_STREAMING, DISPLAY_RESX,
                               DISPLAY_RESY);
@@ -272,7 +295,17 @@ void display_refresh(void) {
   } else {
     SDL_RenderClear(RENDERER);
   }
-  SDL_UpdateTexture(TEXTURE, NULL, BUFFER->pixels, BUFFER->pitch);
+  // Fill BUFFER_TO_DISPLAY with BUFFER data
+  SDL_BlitSurface(BUFFER, NULL, BUFFER_TO_DISPLAY, NULL);
+#if defined TREZOR_MODEL_T
+  // Gamma-correcting the display buffer for model T when wanted
+  if (DO_GAMMA_CORRECTION) {
+    gamma_correct_buffer_to_display();
+  }
+#endif
+  // Show the display buffer
+  SDL_UpdateTexture(TEXTURE, NULL, BUFFER_TO_DISPLAY->pixels,
+                    BUFFER_TO_DISPLAY->pitch);
 #define BACKLIGHT_NORMAL 150
   SDL_SetTextureAlphaMod(TEXTURE,
                          MIN(255, 255 * DISPLAY_BACKLIGHT / BACKLIGHT_NORMAL));