Disable the PPU between the title to main screens

During other transitions like game over and such it might also be needed
to have something similar, but for now this should cut it.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

6 files changed, 92 insertions, 13 deletions

diff --git a/include/globals.s b/include/globals.s
index f4e4861..35665f7 100644
--- a/include/globals.s
+++ b/include/globals.s
@@ -1,8 +1,7 @@
 ;; Global variables used throughout the code base.
 .scope Globals
     ;;;
-    ;; Argument values as defined in https://github.com/mssola/style.nes. Note
-    ;; that these variables can also be used as temporary variables.
+    ;; Argument values reserved passing arguments to functions in memory.
     zp_arg0 = $00
     zp_arg1 = $01
     zp_arg2 = $02
@@ -30,7 +29,8 @@
     ;; |-----+------------+-------------------------------------------------------------|
     ;; |   7 | render     | Game logic is over, block main code until NMI code is over. |
     ;; |   6 | ppu        | PPU registers have to be touched                            |
-    ;; | 5-2 | -          | Unused                                                      |
+    ;; | 5-3 | -          | Unused                                                      |
+    ;; |   2 | title over | We are transitioning from title to game                     |
     ;; | 1-0 | game       | 0: title; 1: game; 2: game over, 3: game over (coin)        |
     zp_flags = $20
 .endscope
diff --git a/include/ppu.s b/include/ppu.s
index dd24422..a9c0ed2 100644
--- a/include/ppu.s
+++ b/include/ppu.s
@@ -9,4 +9,8 @@
     ;; Shadow for the PPU::CONTROL value. Touch this value instead of accessing
     ;; the PPU register directly.
     zp_control = $80
+
+    ;; Shadow for the PPU::MASK value. Touch this value instead of accessing the
+    ;; PPU register directly.
+    zp_mask = $81
 .endscope
diff --git a/src/assets.s b/src/assets.s
index 8e839d3..ffc6585 100644
--- a/src/assets.s
+++ b/src/assets.s
@@ -74,7 +74,30 @@
         dex
         bne @upper_title_bar_loop
 
-        ;; TODO: store back palettes after game over.
+        ;; Update 2nd palette for background. This is redundant upon entering
+        ;; the game, but it makes sense after a game over.
+        lda #$3F
+        sta PPU::ADDRESS
+        lda #$09
+        sta PPU::ADDRESS
+        lda #$28
+        sta PPU::DATA
+        lda #$2C
+        sta PPU::DATA
+        lda #$16
+        sta PPU::DATA
+
+        ;; Update 1st palette for foreground.
+        lda #$3F
+        sta PPU::ADDRESS
+        lda #$11
+        sta PPU::ADDRESS
+        lda #$30
+        sta PPU::DATA
+        lda #$10
+        sta PPU::DATA
+        lda #$30
+        sta PPU::DATA
 
         rts
     .endproc
@@ -82,11 +105,32 @@
     ;; Performs all the needed tricks in order to get the second nametable as
     ;; expected.
     .proc prepare_for_main_screen
-        ;; TODO: second palette for background should be:
-        ;; .byte $0F, $14, $2C, $28
-        ;;
-        ;; TODO: first palette for the foreground should be:
-        ;; .byte $0F, $16, $10, $30
+        bit PPU::STATUS
+
+        ;; Update 2nd palette for background.
+        lda #$3F
+        sta PPU::ADDRESS
+        lda #$09
+        sta PPU::ADDRESS
+        lda #$14
+        sta PPU::DATA
+        lda #$2C
+        sta PPU::DATA
+        lda #$28
+        sta PPU::DATA
+
+        ;; Update 1st palette for foreground.
+        lda #$3F
+        sta PPU::ADDRESS
+        lda #$11
+        sta PPU::ADDRESS
+        lda #$16
+        sta PPU::DATA
+        lda #$10
+        sta PPU::DATA
+        lda #$30
+        sta PPU::DATA
+
         rts
     .endproc
 
diff --git a/src/driver.s b/src/driver.s
index 8b7f8ce..bb0303f 100644
--- a/src/driver.s
+++ b/src/driver.s
@@ -9,7 +9,25 @@
     zp_player_timer = $30
     PLAYER_TIMER_VALUE = HZ * 2
 
+    ;; Switch from the title screen to the main street. Note that this function
+    ;; is to be called with the PPU disabled. If that's not the case, then it
+    ;; will set the proper values to disable it on the next `nmi` call and set
+    ;; the `title over` flag. With that, call again this function so the
+    ;; switching is actually performed.
     .proc switch
+        ;; Some things from here require the PPU to be disabled. Hence, if
+        ;; that's not the case, disable it now. The `ppu` and the `title over`
+        ;; flags are set as well.
+        lda PPU::zp_mask
+        beq @do_switch
+        lda #%01000100
+        ora Globals::zp_flags
+        sta Globals::zp_flags
+        lda #$00
+        sta PPU::zp_mask
+        rts
+
+    @do_switch:
         ;; Get the assets ready for the main screen. That is, make sure that the
         ;; palettes and such are as desired since the title screen needed
         ;; another setup.
@@ -19,6 +37,10 @@
         lda #%10001010
         sta PPU::zp_control
 
+        ;; Enable back the PPU.
+        lda #%00011110
+        sta PPU::zp_mask
+
         ;; Setup the player timer.
         .ifdef PARTIAL
             lda #1
@@ -28,10 +50,10 @@
         sta zp_player_timer
 
         ;; Mark the state of the game as "game". That is, the player has
-        ;; started. Also set the `ppu` flag so the PPU control update takes
-        ;; place.
+        ;; started. Also set the `ppu` flag and unset the `title over` one.
         lda #%01000001
         ora Globals::zp_flags
+        and #%11111011
         sta Globals::zp_flags
 
         rts
diff --git a/src/jetpac.s b/src/jetpac.s
index 66d5457..184374e 100644
--- a/src/jetpac.s
+++ b/src/jetpac.s
@@ -40,8 +40,8 @@
 .include "assets.s"
 .include "background.s"
 .include "player.s"
-.include "driver.s"
 .include "title.s"
+.include "driver.s"
 .include "vectors.s"
 
 .proc main
@@ -72,6 +72,7 @@
 
     ;; Enable back the PPU
     lda #%00011110
+    sta PPU::zp_mask
     sta PPU::MASK
 
 @main_game_loop:
@@ -85,9 +86,15 @@
     jmp @over
 
 @title_screen:
+    ;; If we are in a transitioning state, avoid the update from the title.
+    lda Globals::zp_flags
+    and #%00000100
+    bne @do_switch
+
     jsr Title::update
     beq @set_flags
 
+@do_switch:
     ;; Start was pressed by the player, switch to the main game.
     jsr Driver::switch
     jmp @set_flags
diff --git a/src/vectors.s b/src/vectors.s
index b06f404..b404d98 100644
--- a/src/vectors.s
+++ b/src/vectors.s
@@ -103,7 +103,9 @@
 
     bit PPU::STATUS
 
-    ;; Update the PPU control register with the shadowed value.
+    ;; Update the PPU control/mask registers with shadowed values.
+    lda PPU::zp_mask
+    sta PPU::MASK
     lda PPU::zp_control
     sta PPU::CONTROL