Bilinear texture filteringHEADmain

1 files changed, 79 insertions, 16 deletions

diff --git a/src/swgfx.c b/src/swgfx.c
index 7ade051..c54fdc1 100644
--- a/src/swgfx.c
+++ b/src/swgfx.c
@@ -46,11 +46,15 @@ typedef struct swgfx {
   // before rendering the model's triangles.
   sgMat4       viewProj; // View-projection matrix.
   sgMat4       mvp;      // Model-view-projection matrix.
-  const sgTexture_t* texture;// User-specified texture.
-  sgTexture_t        defaultTexture; // A default for when no texture is provided.
+  const sgImage* texture;// User-specified texture.
+  sgImage        defaultTexture; // A default for when no texture is provided.
   sgPixel            defaultPixel;   // The single-pixel of the default texture.
 } swgfx;
 
+static inline int mod(int a, int m) { return (m + (a % m)) % m; }
+
+static inline R frac(R a) { return a - (R)((int)a); }
+
 static inline R   rmin(R   a, R   b) { return (a <= b) ? a : b; }
 static inline R   rmax(R   a, R   b) { return (a >= b) ? a : b; }
 static inline int imin(int a, int b) { return (a <= b) ? a : b; }
@@ -61,6 +65,8 @@ static inline sgVec2  max2(sgVec2 a, sgVec2 b) { return (sgVec2){.x = rmax(a.x,
 static inline sgVec2i min2i(sgVec2i a, sgVec2i b) { return (sgVec2i){.x = imin(a.x, b.x), .y = imin(a.y, b.y) }; }
 static inline sgVec2i max2i(sgVec2i a, sgVec2i b) { return (sgVec2i){.x = imax(a.x, b.x), .y = imax(a.y, b.y) }; }
 
+static inline sgVec2 frac2(sgVec2 v) { return (sgVec2){frac(v.x), frac(v.y)}; }
+
 static inline sgVec2 add2(sgVec2 a, sgVec2 b) { return (sgVec2){a.x + b.x, a.y + b.y}; }
 static inline sgVec2 scale2(sgVec2 v, R s) { return (sgVec2){v.x * s, v.y * s}; }
 
@@ -71,6 +77,14 @@ static inline R dot3(sgVec3 a, sgVec3 b) { return a.x * b.x + a.y * b.y + a.z *
 static inline R normsq3(sgVec3 v) { return v.x * v.x + v.y * v.y + v.z * v.z; }
 static inline R norm3  (sgVec3 v) { return (R)sqrt(normsq3(v)); }
 
+static inline sgVec4 lerp4(sgVec4 a, sgVec4 b, R t) {
+  return (sgVec4){
+    .x = a.x + t * (b.x - a.x),
+    .y = a.y + t * (b.y - a.y),
+    .z = a.z + t * (b.z - a.z),
+    .w = a.w + t * (b.w - a.w)};
+}
+
 static inline sgVec3 cross3(sgVec3 a, sgVec3 b) {
   return (sgVec3) {
     a.y * b.z - a.z * b.y,
@@ -237,6 +251,13 @@ static inline sgMat4 Mat4Perspective(R fovy, R aspect, R near, R far) {
     0,          0,                 -1,                  0);
 }
 
+static inline sgVec4 PixelToVec4(sgPixel p) {
+  return (sgVec4){(R)p.r / 255.f, (R)p.g / 255.f, (R)p.b / 255.f, (R)p.a / 255.f};
+}
+static inline sgPixel Vec4ToPixel(sgVec4 p) {
+  return (sgPixel){(int)(p.x * 255.f), (int)(p.y * 255.f), (int)(p.z * 255.f), (int)(p.w * 255.f)};
+}
+
 #ifndef _NDEBUG
 static bool InBounds(int width, int height, int x, int y) {
   return (0 <= x) && (x < width) &&
@@ -258,28 +279,70 @@ static inline R* Depth(swgfx* gfx, int x, int y) {
   return gfx->depth + (y * gfx->dims.x) + x;
 }
 
-void SetPixel(swgfx* gfx, const sgVec2i p, sgPixel colour) {
+static inline void SetPixel(swgfx* gfx, const sgVec2i p, sgPixel colour) {
   assert(gfx);
   *Pixel(gfx, p.x, p.y) = colour;
 }
 
-void SetDepth(swgfx* gfx, const sgVec2i p, R depth) {
+static inline void SetDepth(swgfx* gfx, const sgVec2i p, R depth) {
   assert(gfx);
   *Depth(gfx, p.x, p.y) = depth;
 }
 
-// TODO: Mipmapping.
-sgPixel Sample(const sgTexture_t* texture, sgVec2 uv) {
+static inline sgPixel ReadTexture(const sgImage* texture, sgVec2i xy) {
+  assert(texture);
+  assert(texture->pixels);
+  assert(InBounds(texture->width, texture->height, xy.x, xy.y));
+  return texture->pixels[xy.y * texture->width + xy.x];
+}
+// Output normalized to [0,1].
+static inline sgVec4 ReadTextureFloat(const sgImage* texture, sgVec2i xy) {
+  return PixelToVec4(ReadTexture(texture, xy));
+}
+
+static inline sgVec2i TextureRepeat(const sgImage* texture, sgVec2i p) {
+  return (sgVec2i){mod(p.x, texture->width), mod(p.y, texture->height)};
+}
+
+static inline sgPixel SampleNearest(const sgImage* texture, sgVec2 uv) {
+  assert(texture);
+  assert(texture->pixels);
+  const sgVec2i xy = {
+    (int)(uv.x * (R)texture->width),
+    (int)(uv.y * (R)texture->height)};
+  const sgVec2i xy2 = TextureRepeat(texture, xy);
+  return ReadTexture(texture, xy2);
+}
+
+static inline sgPixel SampleBilinear(const sgImage* texture, sgVec2 uv) {
   assert(texture);
   assert(texture->pixels);
-#define INDEX(X,Y) texture->pixels[(Y) * texture->width + (X)]
-  // Doing a nearest sample for now. TODO: Other sampling strategies.
-  const int x = (int)(uv.x * (R)texture->width);
-  const int y = (int)(uv.y * (R)texture->height);
-  // Repeat for now. TODO: Clamping and other strategies.
-  const int xx = x % texture->width;
-  const int yy = y % texture->height;
-  return INDEX(xx,yy);
+#define ADDR(x,y) TextureRepeat(texture, (sgVec2i){x,y})
+  // Find the closest grid vertex, then interpolate the 4 neighbouring pixel
+  // centers.
+  const sgVec2i tl = ADDR(
+    (int)(uv.x * (R)(texture->width  - 1)),
+    (int)(uv.y * (R)(texture->height - 1)));
+  const sgVec2i tr = ADDR(tl.x+1, tl.y);
+  const sgVec2i bl = ADDR(tl.x,   tl.y+1);
+  const sgVec2i br = ADDR(tl.x+1, tl.y+1);
+  const sgVec2   t = frac2(uv);
+  const sgVec4 tl_pix = ReadTextureFloat(texture, tl);
+  const sgVec4 tr_pix = ReadTextureFloat(texture, tr);
+  const sgVec4 bl_pix = ReadTextureFloat(texture, bl);
+  const sgVec4 br_pix = ReadTextureFloat(texture, br);
+  const sgVec4 x1 = lerp4(tl_pix, tr_pix, t.x);
+  const sgVec4 x2 = lerp4(bl_pix, br_pix, t.x);
+  const sgVec4  y = lerp4(x1, x2, t.y);
+  return Vec4ToPixel(y);
+}
+
+// TODO: Mipmapping.
+// TODO: Clamping and other addressing strategies.
+static inline sgPixel Sample(const sgImage* texture, sgVec2 uv) {
+  // TODO: Add a member to sgImage that determines how it should be filtered.
+  //return SampleNearest(texture, uv);
+  return SampleBilinear(texture, uv);
 }
 
 static inline sgAABB2 TriangleAabb2(sgVec2 p0, sgVec2 p1, sgVec2 p2) {
@@ -489,7 +552,7 @@ swgfx* sgNew(int width, int height, void* mem) {
   gfx->colour = SG_ALLOC(&aligned, width * height, sgPixel);
   gfx->depth  = SG_ALLOC(&aligned, width * height, R);
   gfx->defaultPixel   = (sgPixel){255, 255, 255, 255};
-  gfx->defaultTexture = (sgTexture_t){
+  gfx->defaultTexture = (sgImage){
     .width  = 1,
     .height = 1,
     .pixels = &gfx->defaultPixel,
@@ -578,7 +641,7 @@ void sgViewport(swgfx* gfx, int x0, int y0, int width, int height) {
   gfx->viewport = (sgViewport_t){x0, y0, width, height};
 }
 
-void sgTexture(swgfx* gfx, const sgTexture_t* texture) {
+void sgTexture(swgfx* gfx, const sgImage* texture) {
   assert(gfx);
   assert(texture);
   gfx->texture = texture;