File melonds_PR1807.patch of Package melonds

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File melonds_PR1807.patch of Package melonds (Revision a7dc2c74100670636650674da7c8380e)

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From 19a40968682094540ee6028b7a7e169012ea3201 Mon Sep 17 00:00:00 2001
From: Jaklyy <102590697+Jaklyy@users.noreply.github.com>
Date: Thu, 27 Jul 2023 02:23:36 -0400
Subject: [PATCH 1/2] fix certain slopes not having gaps

---
 src/GPU3D_Soft.h | 44 +++++++++++++++++++++++++++++++++-----------
 1 file changed, 33 insertions(+), 11 deletions(-)

diff --git a/src/GPU3D_Soft.h b/src/GPU3D_Soft.h
index 0c6ca4338..e8796f0eb 100644
--- a/src/GPU3D_Soft.h
+++ b/src/GPU3D_Soft.h
@@ -280,7 +280,6 @@ class SoftRenderer : public Renderer3D
             // slope increment has a 18-bit fractional part
             // note: for some reason, x/y isn't calculated directly,
             // instead, 1/y is calculated and then multiplied by x
-            // TODO: this is still not perfect (see for example x=169 y=33)
             if (ylen == 0)
                 Increment = 0;
             else if (ylen == xlen && xlen != 1)
@@ -313,21 +312,41 @@ class SoftRenderer : public Renderer3D
 
             dx += (y - y0) * Increment;
 
+            if (XMajor)
+            {
+                // used for calculating AA coverage
+                xcov_incr = (ylen << 10) / xlen;
+
+                if (side ^ Negative)
+                {
+                    dxold = dx;
+                    // I dont think the first span can have a gap but i think its technically correct to do this calc anyway?
+                    // could probably be removed as a minor optimization
+                    dx &= ~0x1FF;
+                }
+            }
+
             s32 x = XVal();
 
             int interpoffset = (Increment >= 0x40000) && (side ^ Negative);
             Interp.Setup(y0-interpoffset, y1-interpoffset, w0, w1);
             Interp.SetX(y);
 
-            // used for calculating AA coverage
-            if (XMajor) xcov_incr = (ylen << 10) / xlen;
-
             return x;
         }
 
         s32 Step()
-        {
-            dx += Increment;
+        {   
+            if (XMajor && (side ^ Negative)) // tl, br (right side start) & tr, bl (left side start)
+            {
+                // round dx; required to create gaps in lines like on hw
+                // increment using dxold to make the line not completely borked after rendering a gap
+                dx = (dxold & ~0x1FF) + Increment;
+                dxold += Increment;
+            }
+            else
+                dx += Increment;
+
             y++;
 
             s32 x = XVal();
@@ -353,15 +372,18 @@ class SoftRenderer : public Renderer3D
             // only needed for aa calcs, as actual line spans are broken
             if constexpr (!swapped || side)
             {
-                if (side ^ Negative)
-                    *length = (dx >> 18) - ((dx-Increment) >> 18);
-                else
-                    *length = ((dx+Increment) >> 18) - (dx >> 18);
+                if (side ^ Negative) // tr, bl (left side end) & tl br (right side end)
+                // dxold used here to avoid rounding the endpoint
+                *length = (dx >> 18) - (dxold - Increment >> 18);
+                else // tl, br (left side end) & tr, bl (right side end)
+                // dx rounded down to create gaps in lines like on hw
+                *length = ((dx & ~0x1FF) + Increment >> 18) - (dx >> 18);
             }
 
             // for X-major edges, we return the coverage
             // for the first pixel, and the increment for
             // further pixels on the same scanline
+            // TODO: check how coverage interacts with line gaps
             s32 startx = dx >> 18;
             if (Negative) startx = xlen - startx;
             if (side)     startx = startx - *length + 1;
@@ -421,7 +443,7 @@ class SoftRenderer : public Renderer3D
     private:
         s32 x0, xmin, xmax;
         s32 xlen, ylen;
-        s32 dx;
+        s32 dx, dxold;
         s32 y;
 
         s32 xcov_incr;

From d2eb85e69bd72ed6237cf7ad6e554648bd88ec67 Mon Sep 17 00:00:00 2001
From: Jaklyy <102590697+Jaklyy@users.noreply.github.com>
Date: Sun, 27 Aug 2023 12:14:00 -0400
Subject: [PATCH 2/2] slight tweak to comments

---
 src/GPU3D_Soft.h | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/GPU3D_Soft.h b/src/GPU3D_Soft.h
index e8796f0eb..e1fb33f41 100644
--- a/src/GPU3D_Soft.h
+++ b/src/GPU3D_Soft.h
@@ -320,7 +320,8 @@ class SoftRenderer : public Renderer3D
                 if (side ^ Negative)
                 {
                     dxold = dx;
-                    // I dont think the first span can have a gap but i think its technically correct to do this calc anyway?
+                    // I dont think the first span can have a gap but
+                    // I think its technically correct to do this calc anyway?
                     // could probably be removed as a minor optimization
                     dx &= ~0x1FF;
                 }
@@ -337,7 +338,7 @@ class SoftRenderer : public Renderer3D
 
         s32 Step()
         {   
-            if (XMajor && (side ^ Negative)) // tl, br (right side start) & tr, bl (left side start)
+            if (XMajor && (side ^ Negative)) // tl, br = \ (right side end) & tr, bl = / (left side start)
             {
                 // round dx; required to create gaps in lines like on hw
                 // increment using dxold to make the line not completely borked after rendering a gap
@@ -372,10 +373,10 @@ class SoftRenderer : public Renderer3D
             // only needed for aa calcs, as actual line spans are broken
             if constexpr (!swapped || side)
             {
-                if (side ^ Negative) // tr, bl (left side end) & tl br (right side end)
+                if (side ^ Negative) // tr, bl = / (left side end) & tl br = \ (right side start)
                 // dxold used here to avoid rounding the endpoint
                 *length = (dx >> 18) - (dxold - Increment >> 18);
-                else // tl, br (left side end) & tr, bl (right side end)
+                else // tl, br = \ (left side end) & tr, bl = / (right side start)
                 // dx rounded down to create gaps in lines like on hw
                 *length = ((dx & ~0x1FF) + Increment >> 18) - (dx >> 18);
             }
@@ -383,7 +384,7 @@ class SoftRenderer : public Renderer3D
             // for X-major edges, we return the coverage
             // for the first pixel, and the increment for
             // further pixels on the same scanline
-            // TODO: check how coverage interacts with line gaps
+            // TODO: check how coverage interacts with line gaps, I think it's correct though?
             s32 startx = dx >> 18;
             if (Negative) startx = xlen - startx;
             if (side)     startx = startx - *length + 1;

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File melonds_PR1807.patch of Package melonds (Revision a7dc2c74100670636650674da7c8380e)

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