From 21dbca95434d18914b62287c0bb81677c030e6a3 Mon Sep 17 00:00:00 2001
From: RSDuck <rsduck@users.noreply.github.com>
Date: Mon, 16 Nov 2020 15:57:56 +0100
Subject: [PATCH] use proper index buffers

---
 src/GPU3D_OpenGL.cpp | 66 +++++++++++++++++++++++++++-----------------
 1 file changed, 40 insertions(+), 26 deletions(-)

diff --git a/src/GPU3D_OpenGL.cpp b/src/GPU3D_OpenGL.cpp
index 658b2613..8b9f06c5 100644
--- a/src/GPU3D_OpenGL.cpp
+++ b/src/GPU3D_OpenGL.cpp
@@ -74,11 +74,11 @@ typedef struct
     Polygon* PolyData;
 
     u32 NumIndices;
-    u16* Indices;
+    u32 IndicesOffset;
     GLuint PrimType;
 
     u32 NumEdgeIndices;
-    u16* EdgeIndices;
+    u32 EdgeIndicesOffset;
 
     u32 RenderKey;
 
@@ -107,7 +107,11 @@ u32 VertexBuffer[10240 * 7];
 u32 NumVertices;
 
 GLuint VertexArrayID;
+GLuint IndexBufferID;
 u16 IndexBuffer[2048 * 40];
+u32 NumIndices, NumEdgeIndices;
+
+const u32 EdgeIndicesOffset = 2048 * 30;
 
 GLuint TexMemID;
 GLuint TexPalMemID;
@@ -320,6 +324,9 @@ bool Init()
     glEnableVertexAttribArray(3); // attrib
     glVertexAttribIPointer(3, 3, GL_UNSIGNED_INT, 7*4, (void*)(4*4));
 
+    glGenBuffers(1, &IndexBufferID);
+    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IndexBufferID);
+    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(IndexBuffer), NULL, GL_DYNAMIC_DRAW);
 
     glGenFramebuffers(4, &FramebufferID[0]);
     glBindFramebuffer(GL_FRAMEBUFFER, FramebufferID[0]);
@@ -563,15 +570,15 @@ void BuildPolygons(RendererPolygon* polygons, int npolys)
     u32* vptr = &VertexBuffer[0];
     u32 vidx = 0;
 
-    u16* iptr = &IndexBuffer[0];
-    u16* eiptr = &IndexBuffer[2048*30];
+    u32 iidx = 0;
+    u32 eidx = EdgeIndicesOffset;
 
     for (int i = 0; i < npolys; i++)
     {
         RendererPolygon* rp = &polygons[i];
         Polygon* poly = rp->PolyData;
 
-        rp->Indices = iptr;
+        rp->IndicesOffset = iidx;
         rp->NumIndices = 0;
 
         u32 vidx_first = vidx;
@@ -606,7 +613,7 @@ void BuildPolygons(RendererPolygon* polygons, int npolys)
 
                 vptr = SetupVertex(poly, j, vtx, vtxattr, vptr);
 
-                *iptr++ = vidx;
+                IndexBuffer[iidx++] = vidx;
                 rp->NumIndices++;
 
                 vidx++;
@@ -627,9 +634,9 @@ void BuildPolygons(RendererPolygon* polygons, int npolys)
             }
 
             // build a triangle
-            *iptr++ = vidx_first;
-            *iptr++ = vidx - 2;
-            *iptr++ = vidx - 1;
+            IndexBuffer[iidx++] = vidx_first;
+            IndexBuffer[iidx++] = vidx - 2;
+            IndexBuffer[iidx++] = vidx - 1;
             rp->NumIndices += 3;
         }
         else // quad, pentagon, etc
@@ -649,9 +656,9 @@ void BuildPolygons(RendererPolygon* polygons, int npolys)
                     if (j >= 2)
                     {
                         // build a triangle
-                        *iptr++ = vidx_first;
-                        *iptr++ = vidx - 1;
-                        *iptr++ = vidx;
+                        IndexBuffer[iidx++] = vidx_first;
+                        IndexBuffer[iidx++] = vidx - 1;
+                        IndexBuffer[iidx++] = vidx;
                         rp->NumIndices += 3;
                     }
 
@@ -743,46 +750,48 @@ void BuildPolygons(RendererPolygon* polygons, int npolys)
                     if (j >= 1)
                     {
                         // build a triangle
-                        *iptr++ = vidx_first;
-                        *iptr++ = vidx - 1;
-                        *iptr++ = vidx;
+                        IndexBuffer[iidx++] = vidx_first;
+                        IndexBuffer[iidx++] = vidx - 1;
+                        IndexBuffer[iidx++] = vidx;
                         rp->NumIndices += 3;
                     }
 
                     vidx++;
                 }
 
-                *iptr++ = vidx_first;
-                *iptr++ = vidx - 1;
-                *iptr++ = vidx_first + 1;
+                IndexBuffer[iidx++] = vidx_first;
+                IndexBuffer[iidx++] = vidx - 1;
+                IndexBuffer[iidx++] = vidx_first + 1;
                 rp->NumIndices += 3;
             }
         }
 
-        rp->EdgeIndices = eiptr;
+        rp->EdgeIndicesOffset = eidx;
         rp->NumEdgeIndices = 0;
 
         u32 vidx_cur = vidx_first;
         for (int j = 1; j < poly->NumVertices; j++)
         {
-            *eiptr++ = vidx_cur;
-            *eiptr++ = vidx_cur + 1;
+            IndexBuffer[eidx++] = vidx_cur;
+            IndexBuffer[eidx++] = vidx_cur + 1;
             vidx_cur++;
             rp->NumEdgeIndices += 2;
         }
-        *eiptr++ = vidx_cur;
-        *eiptr++ = vidx_first;
+        IndexBuffer[eidx++] = vidx_cur;
+        IndexBuffer[eidx++] = vidx_first;
         rp->NumEdgeIndices += 2;
     }
 
     NumVertices = vidx;
+    NumIndices = iidx;
+    NumEdgeIndices = eidx;
 }
 
 void RenderSinglePolygon(int i)
 {
     RendererPolygon* rp = &PolygonList[i];
 
-    glDrawElements(rp->PrimType, rp->NumIndices, GL_UNSIGNED_SHORT, rp->Indices);
+    glDrawElements(rp->PrimType, rp->NumIndices, GL_UNSIGNED_SHORT, (void*)(uintptr_t)(rp->IndicesOffset * 2));
 }
 
 int RenderPolygonBatch(int i)
@@ -803,7 +812,7 @@ int RenderPolygonBatch(int i)
         numindices += cur_rp->NumIndices;
     }
 
-    glDrawElements(primtype, numindices, GL_UNSIGNED_SHORT, rp->Indices);
+    glDrawElements(primtype, numindices, GL_UNSIGNED_SHORT, (void*)(uintptr_t)(rp->IndicesOffset * 2));
     return numpolys;
 }
 
@@ -823,7 +832,7 @@ int RenderPolygonEdgeBatch(int i)
         numindices += cur_rp->NumEdgeIndices;
     }
 
-    glDrawElements(GL_LINES, numindices, GL_UNSIGNED_SHORT, rp->EdgeIndices);
+    glDrawElements(GL_LINES, numindices, GL_UNSIGNED_SHORT, (void*)(uintptr_t)(rp->EdgeIndicesOffset * 2));
     return numpolys;
 }
 
@@ -1320,6 +1329,11 @@ void RenderFrame()
         glBindBuffer(GL_ARRAY_BUFFER, VertexBufferID);
         glBufferSubData(GL_ARRAY_BUFFER, 0, NumVertices*7*4, VertexBuffer);
 
+        // bind to access the index buffer
+        glBindVertexArray(VertexArrayID);
+        glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, NumIndices * 2, IndexBuffer);
+        glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, EdgeIndicesOffset * 2, NumEdgeIndices * 2, IndexBuffer + EdgeIndicesOffset);
+
         RenderSceneChunk(0, 192);
     }