1 files changed, 64 insertions, 0 deletions

diff --git a/apps/plugins/sdl/progs/wolf3d/wl_parallax.c b/apps/plugins/sdl/progs/wolf3d/wl_parallax.c
new file mode 100644
index 0000000000..8fbc8cfb91
--- /dev/null
+++ b/apps/plugins/sdl/progs/wolf3d/wl_parallax.c
@@ -0,0 +1,64 @@
+#include "version.h"
+
+#ifdef USE_PARALLAX
+
+#include "wl_def.h"
+
+#ifdef USE_FEATUREFLAGS
+
+// The lower left tile of every map determines the start texture of the parallax sky.
+static int GetParallaxStartTexture()
+{
+    int startTex = ffDataBottomLeft;
+    assert(startTex >= 0 && startTex < PMSpriteStart);
+    return startTex;
+}
+
+#else
+
+static int GetParallaxStartTexture()
+{
+    int startTex;
+    switch(gamestate.episode * 10 + mapon)
+    {
+        case  0: startTex = 20; break;
+        default: startTex =  0; break;
+    }
+    assert(startTex >= 0 && startTex < PMSpriteStart);
+    return startTex;
+}
+
+#endif
+
+void DrawParallax(byte *vbuf, unsigned vbufPitch)
+{
+    int startpage = GetParallaxStartTexture();
+    int midangle = player->angle * (FINEANGLES / ANGLES);
+    int skyheight = viewheight >> 1;
+    int curtex = -1;
+    byte *skytex;
+
+    startpage += USE_PARALLAX - 1;
+
+    for(int x = 0; x < viewwidth; x++)
+    {
+        int curang = pixelangle[x] + midangle;
+        if(curang < 0) curang += FINEANGLES;
+        else if(curang >= FINEANGLES) curang -= FINEANGLES;
+        int xtex = curang * USE_PARALLAX * TEXTURESIZE / FINEANGLES;
+        int newtex = xtex >> TEXTURESHIFT;
+        if(newtex != curtex)
+        {
+            curtex = newtex;
+            skytex = PM_GetTexture(startpage - curtex);
+        }
+        int texoffs = TEXTUREMASK - ((xtex & (TEXTURESIZE - 1)) << TEXTURESHIFT);
+        int yend = skyheight - (wallheight[x] >> 3);
+        if(yend <= 0) continue;
+
+        for(int y = 0, offs = x; y < yend; y++, offs += vbufPitch)
+            vbuf[offs] = skytex[texoffs + (y * TEXTURESIZE) / skyheight];
+    }
+}
+
+#endif