[vlc-devel] [PATCH 1/7] opengl: explicitly set swizzle_per_tex values

[Romain Vimont]

In case the texture format is GL_LUMINANCE, swizzle_per_tex was set to
{NULL, "xa"}. Using NULL instead of an explicit swizzle ("x") was a
small optimization to assign the texel value directly:

    vec4 color0 = texture2D(Texture0, TexCoord0);

instead of using the general code generation:

    colors = texture2D(Texture0, TexCoord0);
    val = colors.x;
    vec4 color0 = vec4(val, val, val, 1);

This was possible because the texture exposes the luminance value in
its three components: (L, L, L, 1).

But this special case will disappear when we will rewrite the chroma
conversion using matrix multiplication directly (instead of computing
its steps separately).

This simplifies the logic of the code, and paves the way to refactor
chroma conversion more easily.
---
 .../video_output/opengl/fragment_shaders.c    | 39 +++++++++----------
 1 file changed, 18 insertions(+), 21 deletions(-)

diff --git a/modules/video_output/opengl/fragment_shaders.c b/modules/video_output/opengl/fragment_shaders.c
index f36518972e..ff5481a50b 100644
--- a/modules/video_output/opengl/fragment_shaders.c
+++ b/modules/video_output/opengl/fragment_shaders.c
@@ -290,7 +290,7 @@ opengl_init_swizzle(const struct vlc_gl_interop *interop,
         }
         else
         {
-            swizzle_per_tex[0] = NULL;
+            swizzle_per_tex[0] = "x";
             swizzle_per_tex[1] = "xa";
         }
     }
@@ -484,8 +484,7 @@ opengl_fragment_shader_init(opengl_tex_converter_t *tc, GLenum tex_target,
         ADD("uniform vec4 Coefficients[4];\n");
 
     ADD("uniform vec4 FillColor;\n"
-        "void main(void) {\n"
-        " float val;vec4 colors;\n");
+        "void main(void) {\n");
 
     if (tex_target == GL_TEXTURE_RECTANGLE)
     {
@@ -494,12 +493,15 @@ opengl_fragment_shader_init(opengl_tex_converter_t *tc, GLenum tex_target,
                  "TexCoord%u.y * TexSize%u.y);\n", i, i, i, i, i);
     }
 
-    unsigned color_idx = 0;
-    for (unsigned i = 0; i < interop->tex_count; ++i)
-    {
-        const char *swizzle = swizzle_per_tex[i];
-        if (swizzle)
+    unsigned color_count;
+    if (is_yuv) {
+        ADD(" float val;\n"
+            " vec4 colors;\n");
+        unsigned color_idx = 0;
+        for (unsigned i = 0; i < interop->tex_count; ++i)
         {
+            const char *swizzle = swizzle_per_tex[i];
+            assert(swizzle);
             size_t swizzle_count = strlen(swizzle);
             ADDF(" colors = %s(Texture%u, %s%u);\n", lookup, i, coord_name, i);
             for (unsigned j = 0; j < swizzle_count; ++j)
@@ -511,24 +513,19 @@ opengl_fragment_shader_init(opengl_tex_converter_t *tc, GLenum tex_target,
                 assert(color_idx <= PICTURE_PLANE_MAX);
             }
         }
-        else
-        {
-            ADDF(" vec4 color%u = %s(Texture%u, %s%u);\n",
-                 color_idx, lookup, i, coord_name, i);
-            color_idx++;
-            assert(color_idx <= PICTURE_PLANE_MAX);
-        }
-    }
-    unsigned color_count = color_idx;
-    assert(yuv_space == COLOR_SPACE_UNDEF || color_count == 3);
-
-    if (is_yuv)
         ADD(" vec4 result = (color0 * Coefficients[0]) + Coefficients[3];\n");
+        color_count = color_idx;
+    }
     else
-        ADD(" vec4 result = color0;\n");
+    {
+        ADDF(" vec4 result = %s(Texture0, %s0);\n", lookup, coord_name);
+        color_count = 1;
+    }
+    assert(yuv_space == COLOR_SPACE_UNDEF || color_count == 3);
 
     for (unsigned i = 1; i < color_count; ++i)
     {
+        unsigned color_idx;
         if (yuv_swap_uv)
         {
             assert(color_count == 3);
-- 
2.25.0