Add safe VDC defaults option for homebrew compatibility. #101

Author: drhelius

platforms/libretro/libretro.cpp

@@ -666,6 +666,7 @@ static void set_variabless(void)
         { "geargrafx_lowpass_speed_716", "Video LPF HuC6270 7.16 MHz; Enabled|Disabled" },
         { "geargrafx_lowpass_speed_108", "Video LPF HuC6270 10.8 MHz; Enabled|Disabled" },
         { "geargrafx_no_sprite_limit", "No Sprite Limit; Disabled|Enabled" },
+        { "geargrafx_safe_vdc_defaults", "Safe VDC Defaults (Homebrew); Disabled|Enabled" },
         { "geargrafx_backup_ram", "Backup RAM (restart); Enabled|Disabled" },
         { "geargrafx_deterministic_netplay", "Deterministic Netplay; Disabled|Enabled" },
         { "geargrafx_cdrom_type", "CD-ROM (restart); Auto|Standard|Super CD-ROM|Arcade CD-ROM" },
@@ -990,6 +991,15 @@ static void check_variables(void)
         core->GetHuC6270_2()->SetNoSpriteLimit(strcmp(var.value, "Enabled") == 0);
     }
 
+    var.key = "geargrafx_safe_vdc_defaults";
+    var.value = NULL;
+
+    if (environ_cb(RETRO_ENVIRONMENT_GET_VARIABLE, &var) && var.value)
+    {
+        core->GetHuC6270_1()->SetSafeDefaults(strcmp(var.value, "Enabled") == 0);
+        core->GetHuC6270_2()->SetSafeDefaults(strcmp(var.value, "Enabled") == 0);
+    }
+
     var.key = "geargrafx_avenue_pad_3_switch";
     var.value = NULL;
 

platforms/shared/desktop/config.cpp

@@ -351,6 +351,7 @@ void config_read(void)
     config_video.fps = read_bool("Video", "FPS", false);
     config_video.bilinear = read_bool("Video", "Bilinear", false);
     config_video.sprite_limit = read_bool("Video", "SpriteLimit", false);
+    config_video.safe_vdc_defaults = read_bool("Video", "SafeVdcDefaults", false);
     config_video.mix_frames = read_bool("Video", "MixFrames", true);
     config_video.mix_frames_intensity = read_float("Video", "MixFramesIntensity", 0.50f);
     config_video.scanlines = read_bool("Video", "Scanlines", true);
@@ -619,6 +620,7 @@ void config_write(void)
     write_bool("Video", "FPS", config_video.fps);
     write_bool("Video", "Bilinear", config_video.bilinear);
     write_bool("Video", "SpriteLimit", config_video.sprite_limit);
+    write_bool("Video", "SafeVdcDefaults", config_video.safe_vdc_defaults);
     write_bool("Video", "MixFrames", config_video.mix_frames);
     write_float("Video", "MixFramesIntensity", config_video.mix_frames_intensity);
     write_bool("Video", "Scanlines", config_video.scanlines);

platforms/shared/desktop/config.h

@@ -86,6 +86,7 @@ struct config_Video
     bool fps = false;
     bool bilinear = false;
     bool sprite_limit = false;
+    bool safe_vdc_defaults = false;
     bool mix_frames = true;
     float mix_frames_intensity = 0.50f;
     bool scanlines = true;

platforms/shared/desktop/emu.cpp

@@ -514,6 +514,12 @@ void emu_video_no_sprite_limit(bool enabled)
     geargrafx->GetHuC6270_2()->SetNoSpriteLimit(enabled);
 }
 
+void emu_set_safe_vdc_defaults(bool enabled)
+{
+    geargrafx->GetHuC6270_1()->SetSafeDefaults(enabled);
+    geargrafx->GetHuC6270_2()->SetSafeDefaults(enabled);
+}
+
 void emu_set_overscan(int overscan)
 {
     geargrafx->GetHuC6260()->SetOverscan(overscan == 0 ? false : true);

platforms/shared/desktop/emu.h

@@ -104,6 +104,7 @@ EXTERN void emu_debug_set_callback(GeargrafxCore::GG_Debug_Callback callback);
 EXTERN void emu_set_palette(int palette);
 EXTERN void emu_set_custom_palette(const u8* data);
 EXTERN void emu_video_no_sprite_limit(bool enabled);
+EXTERN void emu_set_safe_vdc_defaults(bool enabled);
 EXTERN void emu_set_overscan(int overscan);
 EXTERN void emu_set_scanline_start_end(int start, int end);
 EXTERN void emu_set_lowpass_filter(bool enabled, float intensity, float cutoff_mhz, bool speed_5_36, bool speed_7_16, bool speed_10_8);

platforms/shared/desktop/gui.cpp

@@ -115,6 +115,7 @@ bool gui_init(void)
     emu_audio_adpcm_volume(config_audio.adpcm_volume);
     emu_set_palette(config_video.palette);
     emu_video_no_sprite_limit(config_video.sprite_limit);
+    emu_set_safe_vdc_defaults(config_video.safe_vdc_defaults);
     emu_set_overscan(config_debug.debug ? 0 : config_video.overscan);
     emu_set_scanline_start_end(
                 config_debug.debug ? 0 : config_video.scanline_start,

platforms/shared/desktop/gui_menus.cpp

@@ -808,6 +808,21 @@ static void menu_video(void)
             emu_video_no_sprite_limit(config_video.sprite_limit);
         }
 
+        if (ImGui::MenuItem("Safe VDC Defaults", "", &config_video.safe_vdc_defaults))
+        {
+            emu_set_safe_vdc_defaults(config_video.safe_vdc_defaults);
+        }
+        if (ImGui::IsItemHovered())
+        {
+            ImGui::BeginTooltip();
+            ImGui::Text("Enable safe VDC register defaults on reset.");
+            ImGui::Text("Useful for homebrew games that don't initialize");
+            ImGui::Text("their own display timing registers.");
+            ImGui::EndTooltip();
+        }
+
+        ImGui::Separator();
+
         ImGui::MenuItem("Bilinear Filtering", "", &config_video.bilinear);
 
         if (ImGui::BeginMenu("Screen Ghosting"))

src/huc6270.cpp

@@ -34,6 +34,8 @@ HuC6270::HuC6270(HuC6280* huC6280)
     m_state.VPOS = &m_vpos;
     m_state.V_STATE = &m_v_state;
     m_state.H_STATE = &m_h_state;
+    m_no_sprite_limit = false;
+    m_safe_defaults = false;
 }
 
 HuC6270::~HuC6270()
@@ -51,8 +53,19 @@ void HuC6270::Init(HuC6260* huC6260, HuC6202* huC6202, GG_Input_Pump_Fn input_pu
 void HuC6270::Reset()
 {
     memset(m_register, 0, sizeof(m_register));
-    m_register[HUC6270_REG_HDR] = 0x1F;
-    m_register[HUC6270_REG_VDR] = 239;
+    if (m_safe_defaults)
+    {
+        m_register[HUC6270_REG_HSR] = 0x0202;
+        m_register[HUC6270_REG_HDR] = 0x041F;
+        m_register[HUC6270_REG_VSR] = 0x0F02;
+        m_register[HUC6270_REG_VDR] = 0x00EF;
+        m_register[HUC6270_REG_VCR] = 0x0004;
+    }
+    else
+    {
+        m_register[HUC6270_REG_HDR] = 0x1F;
+        m_register[HUC6270_REG_VDR] = 239;
+    }
 
     m_address_register = 0;
     m_status_register = 0;

src/huc6270.h

@@ -85,6 +85,7 @@ class HuC6270
     u16* GetVRAM();
     u16* GetSAT();
     void SetNoSpriteLimit(bool no_sprite_limit);
+    void SetSafeDefaults(bool safe_defaults);
     void SaveState(std::ostream& stream);
     void LoadState(std::istream& stream);
 
@@ -146,6 +147,7 @@ class HuC6270
     u16 m_line_buffer_sprites[HUC6270_MAX_BACKGROUND_WIDTH] = {};
     s32 m_line_buffer_index;
     bool m_no_sprite_limit;
+    bool m_safe_defaults;
     s32 m_sprite_count;
     bool m_sprite_overflow;
     HuC6270_Sprite_Data m_sprites[HUC6270_SPRITES * 2] = {};

src/huc6270_inline.h

@@ -75,6 +75,11 @@ INLINE void HuC6270::SetNoSpriteLimit(bool no_sprite_limit)
     m_no_sprite_limit = no_sprite_limit;
 }
 
+INLINE void HuC6270::SetSafeDefaults(bool safe_defaults)
+{
+    m_safe_defaults = safe_defaults;
+}
+
 INLINE u16 HuC6270::ReadVRAM(u16 address)
 {
     if (address < HUC6270_VRAM_SIZE)