Add parallax auto movement

assets/levels/R2/parallax.toml

@@ -3,7 +3,8 @@ width = 256
 height = 32
 u0 = 0
 v0 = 360 # 104 @ BG1
-scrollx = 0.14
+scrollx = 0
+speedx  = 0.14
 y0 = 0
 single = false
 
@@ -12,7 +13,8 @@ width = 256
 height = 16
 u0 = 0
 v0 = 392
-scrollx = 0.16
+scrollx = 0
+speedx = 0.16
 y0 = 32
 single = false
 
@@ -21,7 +23,8 @@ width = 256
 height = 16
 u0 = 0
 v0 = 408
-scrollx = 0.18
+scrollx = 0
+speedx = 0.18
 y0 = 48
 single = false
 

include/parallax.h

@@ -40,11 +40,15 @@ typedef struct {
     uint8_t num_parts;
     uint8_t is_single;
     int32_t scrollx;
+    int32_t speedx;
     int16_t y0;
     ParallaxPart *parts;
 
     // Calculated on load
     uint16_t width;
+
+    // State
+    int32_t rposx;
 } ParallaxStrip;
 
 // Holds all parallax strips for a level

src/parallax.c

@@ -38,7 +38,9 @@ load_parallax(Parallax *parallax, const char *filename)
         strip->num_parts = get_byte(bytes, &b);
         strip->is_single = get_byte(bytes, &b);
         strip->scrollx   = get_long_be(bytes, &b);
+        strip->speedx    = get_long_be(bytes, &b);
         strip->y0        = get_short_be(bytes, &b);
+        strip->rposx     = 0;
 
         strip->parts = alloc_arena_malloc(
             &_level_arena,
@@ -75,11 +77,17 @@ parallax_draw(Parallax *prl, Camera *camera,
         // Cast multiplication to avoid sign extension on bit shift
         // This gets the mult. result but also removes the decimal part
         int32_t stripx = (uint32_t)(camera_vx * strip->scrollx) >> 24;
+
+        // Update strip relative position when there's speed involved
+        strip->rposx -= strip->speedx;
+        if((strip->rposx >> 12) < -((int32_t)strip->width))
+            strip->rposx = 0;
+
         for(uint8_t pi = 0; pi < strip->num_parts; pi++) {
             ParallaxPart *part = &strip->parts[pi];
 
             // Calculate part X position based on factor and camera (int format)
-            int32_t vx = ((int32_t)part->offsetx) - stripx;
+            int32_t vx = ((int32_t)part->offsetx) - stripx + (strip->rposx >> 12);
 
             // Given that each part is a horizontal piece of a strip, we assume
             // that these parts repeat at every (strip width), so just draw

tools/buildprl/buildprl.py

@@ -40,6 +40,7 @@ class ParallaxPart:
 class ParallaxStrip:
     single: bool = False
     scrollx: float = 0
+    speedx: float = 0
     y0: int = 0
     parts: [ParallaxPart] = field(default_factory=list)
 
@@ -47,6 +48,7 @@ class ParallaxStrip:
         f.write(c_ubyte(len(self.parts)))
         f.write(c_ubyte(int(self.single)))
         f.write(c_int(tofixed12(self.scrollx)))
+        f.write(c_int(tofixed12(self.speedx)))
         f.write(c_short(self.y0))
         for p in self.parts:
             p.write_to(f)
@@ -69,6 +71,7 @@ def parse(data) -> Parallax:
         strip = ParallaxStrip()
         strip.single = strip_data.get("single", False)
         strip.scrollx = strip_data.get("scrollx", 0)
+        strip.speedx = strip_data.get("speedx", 0)
         strip.y0 = strip_data.get("y0")
         height = strip_data.get("height")  # Reserved
         parts = strip_data.get("parts")

tools/layouts/prl.hexpat

@@ -12,6 +12,7 @@ struct ParallaxStrip {
        u8 num_parts;
        u8 is_single;
        be s32 scrollx;
+       be s32 speedx;
        be s16 y0;
        ParallaxPart parts[num_parts];
 };