[Decompilation] [th01] EGC-accelerated VRAM page 1➜0 row blitting

Well well, the choice between sorting this function mechanically (and
putting it next to the EGC functions) or contextually (and putting it
next to the GDC SCROLL function)… Any choice would eventually turned
out suboptimal, I'm sure. 😅

Part of P0121, funded by Yanga.

th01/hardware/egc.h

@@ -16,3 +16,8 @@
 void DEFCONV egc_copy_rect_1_to_0_16(
 	screen_x_t x, vram_y_t y, pixel_t w, pixel_t h
 );
+
+// Blits [h] rows starting at [top] from VRAM page 1 to the same position on
+// VRAM page 0. Mainly used after a previous GDC scroll of [h] rows, to
+// smoothly scroll between two full background images.
+void egc_copy_rows_1_to_0(vram_y_t top, pixel_t h);

th01/hardware/egcrows.cpp

@@ -0,0 +1,18 @@
+void egc_copy_rows_1_to_0(vram_y_t top, pixel_t h)
+{
+	vram_offset_t vram_offset = vram_offset_muldiv(0, top);
+	egc_on();
+	egc_setup_copy();
+
+	for(pixel_t y = 0; y < h; y++) {
+		vram_word_amount_t x = 0;
+		while(x < (ROW_SIZE / 2)) {
+			dots16_t page1;
+			graph_accesspage_func(1);	egc_snap(page1, vram_offset, 16);
+			graph_accesspage_func(0);	egc_put(vram_offset, page1, 16);
+			x++;
+			vram_offset += static_cast<vram_offset_t>(sizeof(page1));
+		}
+	}
+	egc_off();
+}

th01/main_13.cpp

@@ -6,9 +6,13 @@
 extern "C" {
 
 #include <dos.h>
+#include "libs/master.lib/master.h"
 #include "platform.h"
 #include "pc98.h"
+#include "planar.h"
+#include "th01/hardware/egc.h"
+#include "th01/hardware/graph.h"
 
 #include "th01/hardware/scrollup.cpp"
-
+#include "th01/hardware/egcrows.cpp"
 }

th01_reiiden.asm

@@ -4558,68 +4558,7 @@ main_13__TEXT	segment	byte public 'CODE' use16
 		assume es:nothing, ss:nothing, ds:_DATA, fs:nothing, gs:nothing
 
 	extern _z_vsync_wait_and_scrollup:proc
-
-; =============== S U B	R O U T	I N E =======================================
-
-; Attributes: bp-based frame
-
-sub_11816	proc far
-
-var_4		= word ptr -4
-var_2		= word ptr -2
-arg_0		= word ptr  6
-arg_2		= word ptr  8
-
-		enter	4, 0
-		push	si
-		push	di
-		mov	ax, [bp+arg_0]
-		imul	ax, 50h
-		mov	si, ax
-		call	egc_on
-		EGC_SETUP_COPY
-		xor	di, di
-		jmp	short loc_11894
-; ---------------------------------------------------------------------------
-
-loc_11857:
-		mov	[bp+var_2], 0
-		jmp	short loc_1188D
-; ---------------------------------------------------------------------------
-
-loc_1185E:
-		push	1
-		call	_graph_accesspage_func
-		les	bx, _VRAM_PLANE_B
-		assume es:nothing
-		add	bx, si
-		mov	ax, es:[bx]
-		mov	[bp+var_4], ax
-		push	0
-		call	_graph_accesspage_func
-		add	sp, 4
-		les	bx, _VRAM_PLANE_B
-		add	bx, si
-		mov	ax, [bp+var_4]
-		mov	es:[bx], ax
-		inc	[bp+var_2]
-		add	si, 2
-
-loc_1188D:
-		cmp	[bp+var_2], 28h	; '('
-		jl	short loc_1185E
-		inc	di
-
-loc_11894:
-		cmp	di, [bp+arg_2]
-		jl	short loc_11857
-		call	egc_off
-		pop	di
-		pop	si
-		leave
-		retf
-sub_11816	endp
-
+	extern _egc_copy_rows_1_to_0:proc
 
 ; =============== S U B	R O U T	I N E =======================================
 
@@ -35010,9 +34949,7 @@ sub_2869E	proc far
 
 loc_28703:
 		call	_z_vsync_wait_and_scrollup stdcall, si
-		push	1
-		push	si
-		call	sub_11816
+		call	_egc_copy_rows_1_to_0 stdcall, si, 1
 		push	1
 		call	_frame_delay
 		add	sp, 8
@@ -42571,9 +42508,7 @@ loc_2D120:
 
 loc_2D12A:
 		call	_z_vsync_wait_and_scrollup stdcall, di
-		push	20h ; ' '
-		push	di
-		call	sub_11816
+		call	_egc_copy_rows_1_to_0 stdcall, di, 32
 		push	1
 		call	_frame_delay
 		add	sp, 8