cc: custom bilinear filtering for YUV quad.

cc/output/shader.cc

Index: cc/output/shader.cc
diff --git a/cc/output/shader.cc b/cc/output/shader.cc
index b5d163862d14e010aa19d5bcd083278366ed34b4..a34ce07bad174bcf9a20f44831f26a2681b267be 100644
--- a/cc/output/shader.cc
+++ b/cc/output/shader.cc
@@ -2028,9 +2028,11 @@ FragmentShaderYUVVideo::FragmentShaderYUVVideo()
       resource_multiplier_location_(-1),
       resource_offset_location_(-1) {}
 
-void FragmentShaderYUVVideo::SetFeatures(bool use_alpha_texture,
+void FragmentShaderYUVVideo::SetFeatures(SamplerType sampler,
+                                         bool use_alpha_texture,
                                          bool use_nv12,
                                          bool use_color_lut) {
+  sampler_ = sampler;
   use_alpha_texture_ = use_alpha_texture;
   use_nv12_ = use_nv12;
   use_color_lut_ = use_color_lut;
@@ -2050,6 +2052,8 @@ void FragmentShaderYUVVideo::Init(GLES2Interface* context,
       "resource_offset",
       "yuv_matrix",
       "yuv_adj",
+      "ya_size",
+      "uv_subsampling_factor",
       "alpha",
       "ya_clamp_rect",
       "uv_clamp_rect",
@@ -2080,9 +2084,14 @@ void FragmentShaderYUVVideo::Init(GLES2Interface* context,
     yuv_matrix_location_ = locations[8];
     yuv_adj_location_ = locations[9];
   }
-  alpha_location_ = locations[10];
-  ya_clamp_rect_location_ = locations[11];
-  uv_clamp_rect_location_ = locations[12];
+  if (sampler_ != SAMPLER_TYPE_2D_RECT) {
+    ya_size_location_ = locations[10];
+  } else {
+    uv_subsampling_factor_location_ = locations[11];
+  }
+  alpha_location_ = locations[12];
+  ya_clamp_rect_location_ = locations[13];
+  uv_clamp_rect_location_ = locations[14];
 }
 
 std::string FragmentShaderYUVVideo::GetShaderString(TexCoordPrecision precision,
@@ -2097,13 +2106,87 @@ std::string FragmentShaderYUVVideo::GetShaderString(TexCoordPrecision precision,
     uniform vec4 ya_clamp_rect;
     uniform vec4 uv_clamp_rect;
   });
-
-  std::string functions = "";
+  // SHADER0 cannot handle #define
+  head += "\n";
+  head += "  #define PLANE_TYPE int\n";
+  head += "  #define YA 1\n";
+  head += "  #define UV 2\n";
+
+  std::string functions = SHADER0([]() {
+    vec2 TextureLookupBilinearInternal(SamplerType sampler, vec2 snap_tex_coord,
+                                       vec2 unit_texel, vec2 factor) {
+      vec2 s1 = TextureLookup(sampler, snap_tex_coord).xy;
+      vec2 s2 =
+          TextureLookup(sampler, snap_tex_coord + vec2(unit_texel.x, 0.)).xy;
+      vec2 s3 =
+          TextureLookup(sampler, snap_tex_coord + vec2(0., unit_texel.y)).xy;
+      vec2 s4 = TextureLookup(sampler, snap_tex_coord + unit_texel).xy;
+      return mix(mix(s1, s2, factor.x), mix(s3, s4, factor.x), factor.y);
+    }
+  });
+  if (sampler_ == SAMPLER_TYPE_2D_RECT) {
+    head += "  uniform vec2 uv_subsampling_factor;\n";
+    functions += SHADER0([]() {
+      vec2 TextureLookupBilinear(SamplerType sampler, vec2 tex_coord,
+                                 PLANE_TYPE type) {
+        vec2 ya_tex_coord = tex_coord;
+        if (type == UV) {
+          ya_tex_coord = tex_coord / uv_subsampling_factor;
+        }
+        vec2 unnorm_tex_coord = ya_tex_coord - vec2(0.5);
+        vec2 f = fract(unnorm_tex_coord);
+        vec2 texel_offset = floor(unnorm_tex_coord) - floor(ya_tex_coord);
+        vec2 unit_texel = vec2(1.);
+        if (type == UV) {
+          texel_offset = texel_offset * uv_subsampling_factor;
+          unit_texel = unit_texel * uv_subsampling_factor;
+        }
+        vec2 snap_tex_coord =
+            floor(tex_coord) + (unit_texel * 0.5) + texel_offset;
+        return TextureLookupBilinearInternal(sampler, snap_tex_coord,
+                                             unit_texel, f);
+      }
+    });
+  } else {
+    head += "  uniform vec2 ya_size;\n";
+    functions += SHADER0([]() {
+      // refer to Mesa sample_2d_linear() in s_texfilter.c
+      // https://cs.chromium.org/chromium/src/third_party/mesa/src/src/mesa/swrast/s_texfilter.c?q=sample_2d_linear&sq=package:chromium
+      //
+      // This shader needs a custom bilinear filter because U plane can be
+      // smaller than Y plane.
+      // For example, look at the following figures. When the current fragment
+      // samples the middle point of (3, 3) texel of Y texture, it points out
+      // upper left of (1, 1) texel of U texture. The default GL_LINEAR samples
+      // 4 texels of U plane, while it samples only (3, 3) texel of Y plane.
+      // TextureLookupBilinear() samples U plane with Y plane fraction to
+      // sample like Y plane.
+      //  Y 4x4      U 2x2    U sampling by GL_LINEAR
+      //  +-+-+-+-+  +--+--+  +--+--+
+      //  | | | | |  |  |  |  |  |  |
+      //  +-------+  |  |  |  | +--++
+      //  | | | | |  +-----+  +-----|
+      //  +-------+  |  |· |  | ||·||
+      //  | | |·| |  |  |  |  | +--+|
+      //  +-------+  +--+--+  +-----+
+      //  | | | | |
+      //  +-+-+-+-+
+      vec2 TextureLookupBilinear(SamplerType sampler, vec2 tex_coord,
+                                 PLANE_TYPE type) {
+        vec2 unit_texel = 1.0 / ya_size;
+        vec2 unnorm_tex_coord = (tex_coord * ya_size) - vec2(0.5);
+        vec2 f = fract(unnorm_tex_coord);
+        vec2 snap_tex_coord = (floor(unnorm_tex_coord) + vec2(0.5)) / ya_size;
+        return TextureLookupBilinearInternal(sampler, snap_tex_coord,
+                                             unit_texel, f);
+      }
+    });
+  }
   if (use_nv12_) {
     head += "  uniform SamplerType uv_texture;\n";
     functions += SHADER0([]() {
       vec2 GetUV(vec2 uv_clamped) {
-        return TextureLookup(uv_texture, uv_clamped).xy;
+        return TextureLookupBilinear(uv_texture, uv_clamped, UV);
       }
     });
   } else {
@@ -2111,8 +2194,8 @@ std::string FragmentShaderYUVVideo::GetShaderString(TexCoordPrecision precision,
     head += "  uniform SamplerType v_texture;\n";
     functions += SHADER0([]() {
       vec2 GetUV(vec2 uv_clamped) {
-        return vec2(TextureLookup(u_texture, uv_clamped).x,
-                    TextureLookup(v_texture, uv_clamped).x);
+        return vec2(TextureLookupBilinear(u_texture, uv_clamped, UV).x,
+                    TextureLookupBilinear(v_texture, uv_clamped, UV).x);
       }
     });
   }
@@ -2121,7 +2204,7 @@ std::string FragmentShaderYUVVideo::GetShaderString(TexCoordPrecision precision,
     head += "  uniform SamplerType a_texture;\n";
     functions += SHADER0([]() {
       float GetAlpha(vec2 ya_clamped) {
-        return alpha * TextureLookup(a_texture, ya_clamped).x;
+        return alpha * TextureLookupBilinear(a_texture, ya_clamped, YA).x;
       }
     });
   } else {
@@ -2165,7 +2248,7 @@ std::string FragmentShaderYUVVideo::GetShaderString(TexCoordPrecision precision,
     void main() {
       vec2 ya_clamped =
           max(ya_clamp_rect.xy, min(ya_clamp_rect.zw, v_yaTexCoord));
-      float y_raw = TextureLookup(y_texture, ya_clamped).x;
+      float y_raw = TextureLookupBilinear(y_texture, ya_clamped, YA).x;
       vec2 uv_clamped =
           max(uv_clamp_rect.xy, min(uv_clamp_rect.zw, v_uvTexCoord));
       vec3 yuv = vec3(y_raw, GetUV(uv_clamped));