examples: Wait for VBL in the right place

This change is a bit pedantic, but it makes the ROMs run better in
DeSmuMe.

Some examples (particularly the dual 3D examples) used to flicker during
one or two seconds right after starting. In dual 3D examples the top and
bottom screen would start swapped, and they would eventually swap and
stop flickering. This would never happen in melonDS or real hardware.

I suspect this is because of the interaction between GFX_FLUSH and
swiWaitForVBlank(), where there would be some timing difference to reach
the first swiWaitForVBlank() or GFX_FLUSH, and that caused the desync.

This commit moves swiWaitForVBlank() to the beginning of the game loop.
This means that, even in the first iteration of the game loop, all
emulators and hardware will be synchronized. This doesn't actually
matter in any other situation, it just makes the first iteration
consistent.

examples/2d_system/gui/source/main.c

@@ -150,6 +150,10 @@ int main(void)
 
     while (1)
     {
+        // Update GUI, input and wait for vertical blank. You have to
+        // call scanKeys() each frame for this to work.
+        NE_WaitForVBL(NE_UPDATE_GUI);
+
         scanKeys(); // This function is needed for the GUI
 
         printf("\x1b[0;0H");
@@ -166,10 +170,6 @@ int main(void)
 
         // Draw things...
         NE_Process(Draw3DScene);
-
-        // Update GUI, input and wait for vertical blank. You have to
-        // call scanKeys() each frame for this to work.
-        NE_WaitForVBL(NE_UPDATE_GUI);
     }
 
     return 0;

examples/2d_system/quad_texture_sizes/source/main.c

@@ -62,8 +62,9 @@ int main(void)
 
     while (1)
     {
-        NE_Process(Draw3DScene);
         NE_WaitForVBL(0);
+
+        NE_Process(Draw3DScene);
     }
 
     return 0;

examples/2d_system/quads/source/main.c

@@ -78,14 +78,16 @@ int main(void)
 
     printf("A: Alpha");
 
-    while (1) {
+    while (1)
+    {
+        NE_WaitForVBL(0);
+
         scanKeys();
         kheld = keysHeld();
 
         UpdateQuads();
 
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/2d_system/sprites/source/main.c

@@ -65,6 +65,8 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         scanKeys();
         uint32 keys = keysHeld();
 
@@ -83,7 +85,6 @@ int main(void)
         NE_SpriteSetPos(Sprite[2], x, y);
 
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/2d_system/text/source/main.c

@@ -72,8 +72,9 @@ int main(void)
 
     while (1)
     {
-        NE_Process(Draw3DScene);
         NE_WaitForVBL(0);
+
+        NE_Process(Draw3DScene);
     }
 
     return 0;

examples/effects/fog/source/main.c

@@ -85,6 +85,8 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         // Refresh keys
         scanKeys();
         uint32 keys = keysDown();
@@ -124,7 +126,6 @@ int main(void)
 
         // Draw scene
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/effects/screen_effects/source/main.c

@@ -65,6 +65,8 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         // Refresh keys
         scanKeys();
         uint32 keys = keysHeld();
@@ -101,7 +103,6 @@ int main(void)
 
         // Draw 3D scenes
         NE_ProcessDual(Draw3DScene, Draw3DScene2);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/effects/shading_alpha_outlining/source/main.c

@@ -85,6 +85,8 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         // Refresh keys
         scanKeys();
         uint32 keys = keysHeld();
@@ -125,7 +127,6 @@ int main(void)
 
         // Draw scene
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/effects/specular_material/source/main.c

@@ -102,6 +102,8 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         // Get keys information
         scanKeys();
         uint32 keys = keysHeld();
@@ -165,7 +167,6 @@ int main(void)
         NE_ShininessTableGenerate(shininess);
 
         NE_ProcessDual(Draw3DScene1, Draw3DScene2);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/loading/animated_model/source/main.c

@@ -58,6 +58,8 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(NE_UPDATE_ANIMATIONS);
+
         scanKeys();
         uint32 keys = keysHeld();
 
@@ -75,7 +77,6 @@ int main(void)
                NE_GetCPUPercent(), f32tofloat(NE_ModelAnimGetFrame(Model)));
 
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(NE_UPDATE_ANIMATIONS);
     }
 
     return 0;

examples/loading/clone_models/source/main.c

@@ -85,13 +85,14 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         // Rotate every model
         for (int i = 0; i < NUM_MODELS; i++)
             NE_ModelRotate(Model[i], -i, i % 5, 5 - i);
 
         // Draw scene
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/loading/compressed_texture/source/main.c

@@ -56,8 +56,9 @@ int main(void)
 
     while (1)
     {
-        NE_Process(Draw3DScene);
         NE_WaitForVBL(0);
+
+        NE_Process(Draw3DScene);
     }
 
     return 0;

examples/loading/filesystem_animated_model/source/main.c

@@ -97,9 +97,11 @@ int main(void)
 
     NE_ClearColorSet(NE_Black, 31, 63);
 
+    printf("\x1b[0;0HPad: Rotate\nSTART: Exit");
+
     while (1)
     {
-        printf("\x1b[0;0HPad: Rotate\nSTART: Exit");
+        NE_WaitForVBL(NE_UPDATE_ANIMATIONS);
 
         scanKeys();
         uint32 keys = keysHeld();
@@ -118,7 +120,6 @@ int main(void)
 
         // Draw scene...
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(NE_UPDATE_ANIMATIONS);
     }
 
     return 0;

examples/loading/filesystem_multiple_textures/source/main.c

@@ -86,6 +86,8 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         scanKeys(); //Get keys information...
         uint32 keys = keysDown();
 
@@ -107,7 +109,6 @@ int main(void)
 
         // Draw scene...
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/loading/incomplete_texture/source/main.c

@@ -74,9 +74,10 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         // Draw 3D scene
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/loading/model_with_vertex_color/source/main.c

@@ -60,6 +60,9 @@ int main(void)
 
     while (1)
     {
+        // Wait for next frame
+        NE_WaitForVBL(0);
+
         // Get keys information
         scanKeys();
         uint32 keys = keysHeld();
@@ -78,8 +81,6 @@ int main(void)
 
         // Draw scene
         NE_Process(Draw3DScene);
-        // Wait for next frame
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/loading/multiple_models/source/main.c

@@ -69,13 +69,14 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         // Rotate every model
         for (int i = 0; i < NUM_MODELS; i++)
             NE_ModelRotate(Model[i], -i, i % 5, 5 - i);
 
         // Draw scene
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/loading/paletted_texture/source/main.c

@@ -65,8 +65,9 @@ int main(void)
 
     while (1)
     {
-        NE_ProcessDual(Draw3DScene, Draw3DScene2);
         NE_WaitForVBL(0);
+
+        NE_ProcessDual(Draw3DScene, Draw3DScene2);
     }
 
     return 0;

examples/loading/simple_model/source/main.c

@@ -68,6 +68,9 @@ int main(void)
 
     while (1)
     {
+        // Wait for next frame
+        NE_WaitForVBL(0);
+
         // Get keys information
         scanKeys();
         uint32 keys = keysHeld();
@@ -86,8 +89,6 @@ int main(void)
 
         // Draw scene
         NE_Process(Draw3DScene);
-        // Wait for next frame
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/other/blended_animations/source/main.c

@@ -70,6 +70,8 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(NE_UPDATE_ANIMATIONS);
+
         scanKeys();
         uint32 keys = keysHeld();
 
@@ -112,7 +114,6 @@ int main(void)
                f32tofloat(NE_ModelAnimSecondaryGetFrame(Model)));
 
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(NE_UPDATE_ANIMATIONS);
     }
 
     return 0;

examples/other/clear_bmp/source/main.c

@@ -76,6 +76,8 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         scanKeys();
         uint32 keys = keysHeld();
 
@@ -98,7 +100,6 @@ int main(void)
             scrollx--;
 
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/other/error_handling/source/main.c

@@ -46,8 +46,9 @@ int main(void)
 
     while (1)
     {
-        NE_Process(Draw3DScene);
         NE_WaitForVBL(0);
+
+        NE_Process(Draw3DScene);
     }
 
     return 0;

examples/other/fps_counter/source/main.c

@@ -70,6 +70,9 @@ int main(void)
 
     while (1)
     {
+        // Wait for next frame
+        NE_WaitForVBL(0);
+
         // Get time
         time_t unixTime = time(NULL);
         struct tm* timeStruct = gmtime((const time_t *)&unixTime);
@@ -101,8 +104,7 @@ int main(void)
             NE_ModelRotate(Model, 0, -2, 0);
 
         NE_Process(Draw3DScene);
-        // Wait for next frame
-        NE_WaitForVBL(0);
+
         // Increase frame count
         fpscount++;
     }

examples/other/free_camera/source/main.c

@@ -59,6 +59,8 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         // Get keys information
         scanKeys();
         uint32 keys = keysHeld();
@@ -87,7 +89,6 @@ int main(void)
             NE_CameraMoveFree(Camera, -0.05, 0, 0);
 
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/other/polygon_drawing/source/main.c

@@ -49,8 +49,9 @@ int main(void)
 
     while (1)
     {
-        NE_Process(Draw3DScene);
         NE_WaitForVBL(0);
+
+        NE_Process(Draw3DScene);
     }
 
     return 0;

examples/other/stylus_texture_drawing_rgb256/source/main.c

@@ -51,13 +51,11 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         scanKeys();
         touchRead(&touch);
 
-        NE_Process(Draw3DScene);
-
-        NE_WaitForVBL(0);
-
         if (keysHeld() & KEY_TOUCH)
         {
             NE_TextureDrawingStart(Material);
@@ -71,6 +69,8 @@ int main(void)
 
             NE_TextureDrawingEnd();
         }
+
+        NE_Process(Draw3DScene);
     }
 
     return 0;

examples/other/stylus_texture_drawing_rgba/source/main.c

@@ -35,12 +35,11 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         scanKeys();
         touchPosition touch;
 
-        NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
-
         if (keysHeld() & KEY_TOUCH)
         {
             // Update stylus coordinates when screen is pressed
@@ -58,6 +57,8 @@ int main(void)
 
             NE_TextureDrawingEnd();
         }
+
+        NE_Process(Draw3DScene);
     }
 
     return 0;

examples/other/swap_3d_dual_screen/source/main.c

@@ -70,8 +70,9 @@ int main(void)
 
     while (1)
     {
-        scanKeys();
+        NE_WaitForVBL(0);
 
+        scanKeys();
         uint16_t keys = keysDown();
 
         if (keys & KEY_A)
@@ -82,7 +83,6 @@ int main(void)
             NE_MainScreenSetOnBottom();
 
         NE_ProcessDual(Draw3DScene, Draw3DScene2);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/other/swap_3d_single_screen/source/main.c

@@ -52,8 +52,9 @@ int main(void)
 
     while (1)
     {
-        scanKeys();
+        NE_WaitForVBL(0);
 
+        scanKeys();
         uint16_t keys = keysDown();
 
         if (keys & KEY_A)
@@ -64,7 +65,6 @@ int main(void)
             NE_MainScreenSetOnBottom();
 
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/other/texture_drawing/source/main.c

@@ -64,8 +64,9 @@ int main(void)
 
     while (1)
     {
-        NE_Process(Draw3DScene);
         NE_WaitForVBL(0);
+
+        NE_Process(Draw3DScene);
     }
 
     return 0;

examples/other/touch_test/source/main.c

@@ -136,6 +136,8 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         scanKeys();
         keys = keysHeld();
 
@@ -196,7 +198,6 @@ int main(void)
         }
 
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/physics/basic/source/main.c

@@ -94,8 +94,9 @@ int main(void)
 
     while (1)
     {
-        NE_Process(Draw3DScene);
         NE_WaitForVBL(NE_UPDATE_PHYSICS);
+
+        NE_Process(Draw3DScene);
     }
 
     return 0;

examples/physics/box_tower/source/main.c

@@ -92,8 +92,9 @@ int main(void)
 
     while (1)
     {
-        NE_Process(Draw3DScene);
         NE_WaitForVBL(NE_UPDATE_PHYSICS);
+
+        NE_Process(Draw3DScene);
     }
 
     return 0;

examples/physics/collision_actions/source/main.c

@@ -95,8 +95,9 @@ int main(void)
 
     while (1)
     {
-        NE_Process(Draw3DScene);
         NE_WaitForVBL(NE_UPDATE_PHYSICS);
+
+        NE_Process(Draw3DScene);
     }
 
     return 0;

examples/templates/3d_dual_screen/source/main.c

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: CC0-1.0
 //
-// SPDX-FileContributor: Antonio Niño Díaz, 2008-2011, 2019, 2022
+// SPDX-FileContributor: Antonio Niño Díaz, 2008-2011, 2019, 2022-2023
 //
 // This file is part of Nitro Engine
 
@@ -26,10 +26,13 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         scanKeys();
 
+        // Your code goes here
+
         NE_ProcessDual(Draw3DScene, Draw3DScene2);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/templates/3d_single_screen/source/main.c

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: CC0-1.0
 //
-// SPDX-FileContributor: Antonio Niño Díaz, 2008-2011, 2019, 2022
+// SPDX-FileContributor: Antonio Niño Díaz, 2008-2011, 2019, 2022-2023
 //
 // This file is part of Nitro Engine
 
@@ -21,10 +21,13 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(0);
+
         scanKeys();
 
+        // Your code goes here
+
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(0);
     }
 
     return 0;

examples/templates/using_nflib/source/main.c

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: CC0-1.0
 //
-// SPDX-FileContributor: Antonio Niño Díaz, 2008-2011, 2019, 2022
+// SPDX-FileContributor: Antonio Niño Díaz, 2008-2011, 2019, 2022-2023
 // SPDX-FileContributor: NightFox, 2009-2011
 //
 // This file is part of Nitro Engine
@@ -200,6 +200,20 @@ int main(void)
 
     while (1)
     {
+        NE_WaitForVBL(NE_UPDATE_ANIMATIONS);
+
+        // At this point we are in the vertical blank period. This is where 2D
+        // elements have to be updated to avoid flickering.
+
+        // Update the scroll of the backgrounds
+        for (int n = 0; n < 3; n ++)
+                NF_ScrollBg(1, n + 1, bg_x[n], 0);
+
+        // Copy shadow OAM copy to the OAM of the 2D sub engine
+        oamUpdate(&oamSub);
+
+        // Start processing a new frame after the 2D elements have been updated.
+
         scanKeys();
         uint32 keys = keysHeld();
 
@@ -259,19 +273,8 @@ int main(void)
         // Refresh shadow OAM copy
         NF_SpriteOamSet(1);
 
-        // Draw scene...
+        // Draw 3D scene
         NE_Process(Draw3DScene);
-        NE_WaitForVBL(NE_UPDATE_ANIMATIONS);
-
-        // At this point we are in the vertical blank period. This is where 2D
-        // entities have to be updated to avoid flickering.
-
-        // Update the scroll of the backgrounds
-        for (int n = 0; n < 3; n ++)
-                NF_ScrollBg(1, n + 1, bg_x[n], 0);
-
-        // Copy shadow OAM copy to the OAM of the 2D sub engine
-        oamUpdate(&oamSub);
     }
 
     return 0;