nv2a: Offset vertices to match HW rounding

Co-authored-by: Erik Abair <[email protected]>
xemu-project · Jul 27, 2024 · 5ce8573 · 5ce8573
1 parent a8d8ef5
commit 5ce8573
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Showing 2 changed files with 25 additions and 6 deletions.
diff --git a/hw/xbox/nv2a/shaders.c b/hw/xbox/nv2a/shaders.c
@@ -753,7 +753,9 @@ GLSL_DEFINE(materialEmissionColor, GLSL_LTCTXA(NV_IGRAPH_XF_LTCTXA_CM_COL) ".xyz
     }
 
     mstring_append(body,
-    "   oPos = invViewport * (tPosition * compositeMat);\n"
+    "   oPos = tPosition * compositeMat;\n"
+    "   oPos.xy = adjust_pixel_center(oPos.xy, oPos.w);\n"
+    "   oPos = invViewport * oPos;\n"
     "   oPos.z = oPos.z * 2.0 - oPos.w;\n");
 
     /* FIXME: Testing */
@@ -857,6 +859,26 @@ GLSL_DEFINE(texMat3, GLSL_C_MAT4(NV_IGRAPH_XF_XFCTX_T3MAT))
     }
     mstring_append(header, "\n");
 
+    mstring_append_fmt(header, "\n"
+            "vec2 adjust_pixel_center(vec2 screen_pos, float w) {\n"
+            "  if (w == 0.0 || isinf(w)) {\n"
+            "    w = 1.0;\n"
+            "  }\n"
+
+            "  screen_pos /= w;\n"
+            "  vec2 pixel = floor(screen_pos);\n"
+            "  vec2 subpixel = screen_pos - pixel;\n"
+            "  vec2 round_down = vec2(lessThan(subpixel, vec2(0.5625)));\n"
+
+            "  subpixel -= vec2(0.0625);\n"
+
+            "  vec2 bias = vec2(0.002);\n"
+            "  subpixel += mix(bias, -bias, round_down);\n"
+
+            "  return w * (pixel + subpixel);\n"
+            "}\n"
+            );
+
     MString *body = mstring_from_str("void main() {\n");
 
     for (i = 0; i < NV2A_VERTEXSHADER_ATTRIBUTES; i++) {
@@ -985,12 +1007,10 @@ GLSL_DEFINE(texMat3, GLSL_C_MAT4(NV_IGRAPH_XF_XFCTX_T3MAT))
                        shade_model_mult,
                        shade_model_mult);
 
-
     /* Return combined header + source */
     mstring_append(header, mstring_get_str(body));
     mstring_unref(body);
     return header;
-
 }
 
 static GLuint create_gl_shader(GLenum gl_shader_type,

diff --git a/hw/xbox/nv2a/vsh.c b/hw/xbox/nv2a/vsh.c
@@ -840,10 +840,9 @@ void vsh_translate(uint16_t version,
     mstring_append(body,
         /* the shaders leave the result in screen space, while
          * opengl expects it in clip space.
-         * TODO: the pixel-center co-ordinate differences should handled
          */
-        "  oPos.x = 2.0 * (oPos.x - surfaceSize.x * 0.5) / surfaceSize.x;\n"
-        "  oPos.y = -2.0 * (oPos.y - surfaceSize.y * 0.5) / surfaceSize.y;\n"
+        "  oPos.xy = 2.0 * adjust_pixel_center(oPos.xy, 1.0) / surfaceSize - vec2(1.0);\n"
+        "  oPos.y *= -1;\n"
     );
     if (z_perspective) {
         mstring_append(body, "  oPos.z = oPos.w;\n");