ogc: remove sub-pixel adjustment when drawing triangles and quads

The adjustment is not needed, since the drawn geometries are exactly
delimited by their vertices. The only adjustment that needs to be made
is when drawing lines and point, due to the fact that in these cases the
vertices do not really delimit the geometry, which is instead drawn
around them.

Author: mardy

src/render/ogc/SDL_render_ogc.c

@@ -554,6 +554,8 @@ int OGC_RenderPrimitive(SDL_Renderer *renderer, u8 primitive,
     OGC_RenderData *data = renderer->driverdata;
     size_t count = cmd->data.draw.count;
     const SDL_FPoint *verts = (SDL_FPoint *)(vertices + cmd->data.draw.first);
+    Mtx mv;
+    bool did_change_matrix = false;
     GXColor c = {
         cmd->data.draw.r,
         cmd->data.draw.g,
@@ -564,6 +566,14 @@ int OGC_RenderPrimitive(SDL_Renderer *renderer, u8 primitive,
     data->ops_after_present++;
     OGC_SetBlendMode(renderer, cmd->data.draw.blend);
 
+    if (primitive == GX_LINESTRIP || primitive == GX_POINTS) {
+        float adjustment = 0.5;
+        guMtxIdentity(mv);
+        guMtxTransApply(mv, mv, adjustment, adjustment, 0);
+        GX_LoadPosMtxImm(mv, GX_PNMTX0);
+        did_change_matrix = true;
+    }
+
     /* TODO: optimize state changes. */
     GX_SetTevColor(GX_TEVREG0, c);
     GX_SetTevColorIn(GX_TEVSTAGE0, GX_CC_C0, GX_CC_ZERO, GX_CC_ZERO, GX_CC_ZERO);
@@ -592,6 +602,11 @@ int OGC_RenderPrimitive(SDL_Renderer *renderer, u8 primitive,
         GX_End();
     }
 
+    if (did_change_matrix) {
+        guMtxIdentity(mv);
+        GX_LoadPosMtxImm(mv, GX_PNMTX0);
+    }
+
     return 0;
 }
 

src/video/ogc/SDL_ogcgxcommon.c

@@ -54,20 +54,8 @@ void OGC_set_viewport(int x, int y, int w, int h)
 
 void OGC_draw_init(int w, int h)
 {
-    Mtx mv;
-
     SDL_LogDebug(SDL_LOG_CATEGORY_VIDEO, "OGC_draw_init called with %d, %d", w, h);
 
-    guMtxIdentity(mv);
-    /* Ideally we would use 0.5 to center the coordinates on the pixels, but
-     * this causes some visual artifacts due to rounding: in the VVVVVV game,
-     * all 8x8 pixel textures lose their rightmost column and bottom row,
-     * except when they are drawn on the bottom-right quadrant of the screen.
-     * Values from 0.1 to 0.4 fix this issue, while preserving pixel accuracy
-     * on drawing operations. */
-    guMtxTransApply(mv, mv, 0.4, 0.4, 0);
-    GX_LoadPosMtxImm(mv, GX_PNMTX0);
-
     GX_ClearVtxDesc();
     GX_SetVtxDesc(GX_VA_POS, GX_DIRECT);
     GX_SetVtxDesc(GX_VA_TEX0, GX_INDEX8);