[ppu] oam: Respect per-scanline cycle budget (fixes #98)

source/emulator/core/hw/ppu/render/oam.cpp

@@ -5,6 +5,8 @@
  * Refer to the included LICENSE file.
  */
 
+#include <common/log.hpp>
+
 #include "../ppu.hpp"
 
 namespace nba::core {
@@ -49,6 +51,9 @@ void PPU::RenderLayerOAM(bool bitmap_mode) {
 
   line_contains_alpha_obj = false;
 
+  int cycles = 0;
+  int cycle_limit = mmio.dispcnt.hblank_oam_access ? 954 : 1210;
+
   /* TODO: check if there is a faster way to initialize the array. */
   for (int x = 0; x < 240; x++) {
     buffer_obj[x].priority = 4;
@@ -102,6 +107,8 @@ void PPU::RenderLayerOAM(bool bitmap_mode) {
     x += half_width;
     y += half_height;
 
+    int cycles_per_pixel = 1;
+
     /* Load transform matrix. */
     if (affine) {
       int group = ((attr1 >> 9) & 0x1F) << 5;
@@ -121,6 +128,8 @@ void PPU::RenderLayerOAM(bool bitmap_mode) {
         half_width  *= 2;
         half_height *= 2;
       }
+
+      cycles_per_pixel = 2;
     } else {
       /* Set transform to identity:
        * [ 1 0 ]
@@ -139,6 +148,12 @@ void PPU::RenderLayerOAM(bool bitmap_mode) {
       continue;
     }
 
+    if (affine) {
+      cycles += 10 + 2 * rect_width;
+    } else {
+      cycles += width;
+    }
+
     int local_y = line - y;
     int number  =  attr2 & 0x3FF;
     int palette = (attr2 >> 12) + 16;
@@ -162,11 +177,21 @@ void PPU::RenderLayerOAM(bool bitmap_mode) {
       local_y -= mmio.mosaic.obj._counter_y;
     }
 
+    if (affine) {
+      cycles += 10;
+    }
+
     /* Render OBJ scanline. */
     for (int local_x = -half_width; local_x <= half_width; local_x++) {
       int _local_x = local_x - mosaic_x;
       int global_x = local_x + x;
 
+      if (cycles > cycle_limit) {
+        return;
+      }
+
+      cycles += cycles_per_pixel;
+
       if (mosaic && (++mosaic_x == mmio.mosaic.obj.size_x)) {
         mosaic_x = 0;
       }