[Mesa-dev] [PATCH 04/22] mesa: Add decoding functions for GL_COMPRESSED_SRGB8_ETC2

[Anuj Phogat]

v2: Use MESA_FORMAT_SARGB8 to store the decoded texture data
Signed-off-by: Anuj Phogat <anuj.phogat at gmail.com>
---
 src/mesa/main/texcompress_etc.c |  109 +++++++++++++++++++++++++++++++++++++--
 src/mesa/main/texcompress_etc.h |    7 +++
 2 files changed, 112 insertions(+), 4 deletions(-)

diff --git a/src/mesa/main/texcompress_etc.c b/src/mesa/main/texcompress_etc.c
index bf43edb..eacfb0d 100644
--- a/src/mesa/main/texcompress_etc.c
+++ b/src/mesa/main/texcompress_etc.c
@@ -456,6 +456,33 @@ etc2_rgb8_fetch_texel(const struct etc2_block *block,
   }
 }
 
+/**
+ * Convert an 8-bit sRGB value from non-linear space to a
+ * linear RGB value in [0, 1].
+ * Implemented with a 256-entry lookup table.
+ */
+static inline GLfloat
+nonlinear_to_linear(GLubyte cs8)
+{
+   static GLfloat table[256];
+   static GLboolean tableReady = GL_FALSE;
+   if (!tableReady) {
+      /* compute lookup table now */
+      GLuint i;
+      for (i = 0; i < 256; i++) {
+         const GLfloat cs = UBYTE_TO_FLOAT(i);
+         if (cs <= 0.04045) {
+            table[i] = cs / 12.92f;
+         }
+         else {
+            table[i] = (GLfloat) pow((cs + 0.055) / 1.055, 2.4);
+         }
+      }
+      tableReady = GL_TRUE;
+   }
+   return table[cs8];
+}
+
 static void
 etc2_unpack_rgb8(uint8_t *dst_row,
                  unsigned dst_stride,
@@ -490,6 +517,46 @@ etc2_unpack_rgb8(uint8_t *dst_row,
    }
 }
 
+static void
+etc2_unpack_srgb8(uint8_t *dst_row,
+                  unsigned dst_stride,
+                  const uint8_t *src_row,
+                  unsigned src_stride,
+                  unsigned width,
+                  unsigned height)
+{
+   const unsigned bw = 4, bh = 4, bs = 8, comps = 4;
+   struct etc2_block block;
+   unsigned x, y, i, j;
+   uint8_t tmp;
+
+   for (y = 0; y < height; y += bh) {
+      const uint8_t *src = src_row;
+
+      for (x = 0; x < width; x+= bw) {
+         etc2_rgb8_parse_block(&block, src);
+
+         for (j = 0; j < bh; j++) {
+            uint8_t *dst = dst_row + (y + j) * dst_stride + x * comps;
+            for (i = 0; i < bw; i++) {
+               etc2_rgb8_fetch_texel(&block, i, j, dst,
+                                     false /* punchthrough_alpha */);
+               /* Convert to MESA_FORMAT_SARGB8 */
+	       tmp = dst[0];
+               dst[0] = dst[2];
+               dst[2] = tmp;
+               dst[3] = 255;
+
+               dst += comps;
+            }
+         }
+         src += bs;
+       }
+
+      src_row += src_stride;
+    }
+}
+
 /* ETC2 texture formats are valid in glCompressedTexImage2D and
  * glCompressedTexSubImage2D functions */
 GLboolean
@@ -500,6 +567,14 @@ _mesa_texstore_etc2_rgb8(TEXSTORE_PARAMS)
    return GL_FALSE;
 }
 
+GLboolean
+_mesa_texstore_etc2_srgb8(TEXSTORE_PARAMS)
+{
+   ASSERT(0);
+
+   return GL_FALSE;
+}
+
 void
 _mesa_fetch_texel_2d_f_etc2_rgb8(const struct swrast_texture_image *texImage,
                                  GLint i, GLint j, GLint k, GLfloat *texel)
@@ -520,9 +595,30 @@ _mesa_fetch_texel_2d_f_etc2_rgb8(const struct swrast_texture_image *texImage,
    texel[ACOMP] = 1.0f;
 }
 
+void
+_mesa_fetch_texel_2d_f_etc2_srgb8(const struct swrast_texture_image *texImage,
+                                  GLint i, GLint j, GLint k, GLfloat *texel)
+{
+   struct etc2_block block;
+   GLubyte dst[3];
+   const GLubyte *src;
+
+   src = (const GLubyte *) texImage->Map +
+      (((texImage->RowStride + 3) / 4) * (j / 4) + (i / 4)) * 8;
+
+   etc2_rgb8_parse_block(&block, src);
+   etc2_rgb8_fetch_texel(&block, i % 4, j % 4, dst);
+
+   texel[RCOMP] = nonlinear_to_linear(dst[0]);
+   texel[GCOMP] = nonlinear_to_linear(dst[1]);
+   texel[BCOMP] = nonlinear_to_linear(dst[2]);
+   texel[ACOMP] = 1.0f;
+}
 
 /**
- * Decode texture data in format `MESA_FORMAT_ETC2_RGB8`
+ * Decode texture data in any one of following formats:
+ * `MESA_FORMAT_ETC2_RGB8`
+ * `MESA_FORMAT_ETC2_SRGB8`
  *
  * The size of the source data must be a multiple of the ETC2 block size
  * even if the texture image's dimensions are not aligned to 4.
@@ -541,7 +637,12 @@ _mesa_unpack_etc2_format(uint8_t *dst_row,
                          unsigned src_height,
                          gl_format format)
 {
-   etc2_unpack_rgb8(dst_row, dst_stride,
-                    src_row, src_stride,
-                    src_width, src_height);
+   if (format == MESA_FORMAT_ETC2_RGB8)
+      etc2_unpack_rgb8(dst_row, dst_stride,
+                       src_row, src_stride,
+                       src_width, src_height);
+   else if (format == MESA_FORMAT_ETC2_SRGB8)
+      etc2_unpack_srgb8(dst_row, dst_stride,
+                        src_row, src_stride,
+                        src_width, src_height);
 }
diff --git a/src/mesa/main/texcompress_etc.h b/src/mesa/main/texcompress_etc.h
index 2508f5f..1dc1d5a 100644
--- a/src/mesa/main/texcompress_etc.h
+++ b/src/mesa/main/texcompress_etc.h
@@ -37,6 +37,9 @@ _mesa_texstore_etc1_rgb8(TEXSTORE_PARAMS);
 GLboolean
 _mesa_texstore_etc2_rgb8(TEXSTORE_PARAMS);
 
+GLboolean
+_mesa_texstore_etc2_srgb8(TEXSTORE_PARAMS);
+
 void
 _mesa_fetch_texel_2d_f_etc1_rgb8(const struct swrast_texture_image *texImage,
                                  GLint i, GLint j, GLint k, GLfloat *texel);
@@ -44,6 +47,10 @@ void
 _mesa_fetch_texel_2d_f_etc2_rgb8(const struct swrast_texture_image *texImage,
                                  GLint i, GLint j, GLint k, GLfloat *texel);
 void
+_mesa_fetch_texel_2d_f_etc2_srgb8(const struct swrast_texture_image *texImage,
+                                  GLint i, GLint j, GLint k, GLfloat *texel);
+
+void
 _mesa_etc1_unpack_rgba8888(uint8_t *dst_row,
                            unsigned dst_stride,
                            const uint8_t *src_row,
-- 
1.7.7.6