From c42e1f28d679d9764f24cddeae755c8c036f1c4d Mon Sep 17 00:00:00 2001
From: joevt <joevt@shaw.ca>
Date: Wed, 28 Feb 2024 16:08:32 -0800
Subject: [PATCH] atimach64gx: Fix fb_pitch calculation.

Also, move the calculation to crtc_update where we calculate everything else (including bits per pixel which is needed for the fb_pitch calculation.
---
 devices/video/atimach64gx.cpp | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/devices/video/atimach64gx.cpp b/devices/video/atimach64gx.cpp
index a4ec6f4..310ed05 100644
--- a/devices/video/atimach64gx.cpp
+++ b/devices/video/atimach64gx.cpp
@@ -378,8 +378,7 @@ void AtiMach64Gx::write_reg(uint32_t reg_offset, uint32_t value, uint32_t size)
         break;
     case ATI_CRTC_OFF_PITCH:
         new_value = value;
-        this->fb_pitch = extract_bits<uint32_t>(new_value, ATI_CRTC_PITCH, ATI_CRTC_PITCH_size) * 8;
-        this->fb_ptr = &this->vram_ptr[extract_bits<uint32_t>(new_value, ATI_CRTC_OFFSET, ATI_CRTC_OFFSET_size) * 8];
+        this->crtc_update();
         return;
     case ATI_CRTC_INT_CNTL:
     {
@@ -609,6 +608,19 @@ void AtiMach64Gx::crtc_update()
         need_recalc = true;
     }
 
+    static uint8_t bits_per_pixel[8] = {0, 0, 4, 8, 16, 24, 32, 0};
+
+    int new_fb_pitch = extract_bits<uint32_t>(this->regs[ATI_CRTC_OFF_PITCH], ATI_CRTC_PITCH, ATI_CRTC_PITCH_size) * bits_per_pixel[this->pixel_format];
+    if (new_fb_pitch != this->fb_pitch) {
+        this->fb_pitch = new_fb_pitch;
+        need_recalc = true;
+    }
+    uint8_t* new_fb_ptr = &this->vram_ptr[extract_bits<uint32_t>(this->regs[ATI_CRTC_OFF_PITCH], ATI_CRTC_OFFSET, ATI_CRTC_OFFSET_size) * 8];
+    if (new_fb_ptr != this->fb_ptr) {
+        this->fb_ptr = new_fb_ptr;
+        need_recalc = true;
+    }
+
     // pixel clock = source_freq / post_div
     int m = 8 >> (this->dac_regs[Rgb514::F0_M0] >> 6);
     int vco_div = (this->dac_regs[Rgb514::F0_M0] & 0x3F) + 65;