cogl: Set LOD bias to -0.5 for single mipmap modes

So that whenever forced to choose between two levels of detail (two mipmaps)
we will land on the sharpest looking one (highest resolution). That's the
mipmap level equal to the floor of the current level of detail requested.

Closes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5920
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2644>

9 files changed, 56 insertions, 0 deletions

diff --git a/cogl/cogl/cogl-private.h b/cogl/cogl/cogl-private.h
index 5a714fc1a..f842047f0 100644
--- a/cogl/cogl/cogl-private.h
+++ b/cogl/cogl/cogl-private.h
@@ -57,6 +57,7 @@ typedef enum
   COGL_PRIVATE_FEATURE_ALPHA_TEXTURES,
   COGL_PRIVATE_FEATURE_TEXTURE_SWIZZLE,
   COGL_PRIVATE_FEATURE_TEXTURE_MAX_LEVEL,
+  COGL_PRIVATE_FEATURE_TEXTURE_LOD_BIAS,
   COGL_PRIVATE_FEATURE_OES_EGL_SYNC,
   /* If this is set then the winsys is responsible for queueing dirty
    * events. Otherwise a dirty event will be queued when the onscreen
diff --git a/cogl/cogl/driver/gl/cogl-pipeline-opengl.c b/cogl/cogl/driver/gl/cogl-pipeline-opengl.c
index 8986e0466..d1e76f965 100644
--- a/cogl/cogl/driver/gl/cogl-pipeline-opengl.c
+++ b/cogl/cogl/driver/gl/cogl-pipeline-opengl.c
@@ -682,6 +682,22 @@ _cogl_sampler_gl_init (CoglContext *context, CoglSamplerCacheEntry *entry)
       GE (context, glSamplerParameteri (entry->sampler_object,
                                         GL_TEXTURE_WRAP_T,
                                         entry->wrap_mode_t) );
+
+      /* While COGL_PRIVATE_FEATURE_SAMPLER_OBJECTS implies support for
+       * GL_TEXTURE_LOD_BIAS in GL, the same is not true in GLES. So check,
+       * and also only apply GL_TEXTURE_LOD_BIAS in mipmap modes:
+       */
+      if (_cogl_has_private_feature (context,
+                                     COGL_PRIVATE_FEATURE_TEXTURE_LOD_BIAS) &&
+          entry->min_filter != GL_NEAREST &&
+          entry->min_filter != GL_LINEAR)
+        {
+          GLfloat bias = _cogl_texture_min_filter_get_lod_bias (entry->min_filter);
+
+          GE (context, glSamplerParameterf (entry->sampler_object,
+                                            GL_TEXTURE_LOD_BIAS,
+                                            bias));
+        }
     }
   else
     {
diff --git a/cogl/cogl/driver/gl/cogl-texture-2d-gl.c b/cogl/cogl/driver/gl/cogl-texture-2d-gl.c
index 23111eabf..61ccd75cf 100644
--- a/cogl/cogl/driver/gl/cogl-texture-2d-gl.c
+++ b/cogl/cogl/driver/gl/cogl-texture-2d-gl.c
@@ -470,6 +470,15 @@ _cogl_texture_2d_gl_flush_legacy_texobj_filters (CoglTexture *tex,
                                    tex_2d->gl_texture);
   GE( ctx, glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, mag_filter) );
   GE( ctx, glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, min_filter) );
+
+  if (_cogl_has_private_feature (ctx, COGL_PRIVATE_FEATURE_TEXTURE_LOD_BIAS) &&
+      min_filter != GL_NEAREST &&
+      min_filter != GL_LINEAR)
+    {
+      GLfloat bias = _cogl_texture_min_filter_get_lod_bias (min_filter);
+
+      GE (ctx, glTexParameterf (GL_TEXTURE_2D, GL_TEXTURE_LOD_BIAS, bias));
+    }
 }
 
 void
diff --git a/cogl/cogl/driver/gl/cogl-texture-gl-private.h b/cogl/cogl/driver/gl/cogl-texture-gl-private.h
index a8fbd2866..7804f8e7e 100644
--- a/cogl/cogl/driver/gl/cogl-texture-gl-private.h
+++ b/cogl/cogl/driver/gl/cogl-texture-gl-private.h
@@ -62,4 +62,11 @@ _cogl_texture_gl_generate_mipmaps (CoglTexture *texture);
 GLenum
 _cogl_texture_gl_get_format (CoglTexture *texture);
 
+static inline GLfloat
+_cogl_texture_min_filter_get_lod_bias (GLenum min_filter)
+{
+  return (min_filter == GL_NEAREST_MIPMAP_NEAREST ||
+          min_filter == GL_LINEAR_MIPMAP_NEAREST) ? -0.5f : 0.0f;
+}
+
 #endif /* _COGL_TEXTURE_GL_PRIVATE_H_ */
diff --git a/cogl/cogl/driver/gl/cogl-util-gl-private.h b/cogl/cogl/driver/gl/cogl-util-gl-private.h
index be8fa1eeb..2929e1c2d 100644
--- a/cogl/cogl/driver/gl/cogl-util-gl-private.h
+++ b/cogl/cogl/driver/gl/cogl-util-gl-private.h
@@ -250,4 +250,8 @@ cogl_gl_get_gpu_time_ns (CoglContext *context);
 #define GL_QUERY_RESULT 0x8866
 #endif
 
+#ifndef GL_TEXTURE_LOD_BIAS
+#define GL_TEXTURE_LOD_BIAS 0x8501
+#endif
+
 #endif /* _COGL_UTIL_GL_PRIVATE_H_ */
diff --git a/cogl/cogl/driver/gl/gl/cogl-driver-gl.c b/cogl/cogl/driver/gl/gl/cogl-driver-gl.c
index e498263aa..7c9449f5b 100644
--- a/cogl/cogl/driver/gl/gl/cogl-driver-gl.c
+++ b/cogl/cogl/driver/gl/gl/cogl-driver-gl.c
@@ -526,6 +526,13 @@ _cogl_driver_update_features (CoglContext *ctx,
   COGL_FLAGS_SET (private_features,
                   COGL_PRIVATE_FEATURE_TEXTURE_MAX_LEVEL, TRUE);
 
+  if (COGL_CHECK_GL_VERSION (gl_major, gl_minor, 3, 1) ||
+      _cogl_check_extension ("GL_EXT_texture_lod_bias", gl_extensions))
+    {
+      COGL_FLAGS_SET (private_features,
+                      COGL_PRIVATE_FEATURE_TEXTURE_LOD_BIAS, TRUE);
+    }
+
   if (ctx->glFenceSync)
     COGL_FLAGS_SET (ctx->features, COGL_FEATURE_ID_FENCE, TRUE);
 
diff --git a/cogl/cogl/driver/gl/gles/cogl-driver-gles.c b/cogl/cogl/driver/gl/gles/cogl-driver-gles.c
index de080a99d..0904f5a04 100644
--- a/cogl/cogl/driver/gl/gles/cogl-driver-gles.c
+++ b/cogl/cogl/driver/gl/gles/cogl-driver-gles.c
@@ -437,6 +437,12 @@ _cogl_driver_update_features (CoglContext *context,
                     COGL_FEATURE_ID_TEXTURE_RG,
                     TRUE);
 
+  if (_cogl_check_extension ("GL_EXT_texture_lod_bias", gl_extensions))
+    {
+      COGL_FLAGS_SET (private_features,
+                      COGL_PRIVATE_FEATURE_TEXTURE_LOD_BIAS, TRUE);
+    }
+
   if (context->glGenQueries && context->glQueryCounter && context->glGetInteger64v)
     COGL_FLAGS_SET (context->features, COGL_FEATURE_ID_TIMESTAMP_QUERY, TRUE);
 
diff --git a/cogl/cogl/gl-prototypes/cogl-all-functions.h b/cogl/cogl/gl-prototypes/cogl-all-functions.h
index fe9feaa5c..f98ea02f6 100644
--- a/cogl/cogl/gl-prototypes/cogl-all-functions.h
+++ b/cogl/cogl/gl-prototypes/cogl-all-functions.h
@@ -178,6 +178,10 @@ COGL_EXT_FUNCTION (void, glSamplerParameteri,
                    (GLuint sampler,
                     GLenum pname,
                     GLint param))
+COGL_EXT_FUNCTION (void, glSamplerParameterf,
+                   (GLuint sampler,
+                    GLenum pname,
+                    GLfloat param))
 COGL_EXT_END ()
 
 COGL_EXT_BEGIN (only_gl3, 3, 0,
diff --git a/cogl/cogl/gl-prototypes/cogl-core-functions.h b/cogl/cogl/gl-prototypes/cogl-core-functions.h
index e04b443ae..e362e797d 100644
--- a/cogl/cogl/gl-prototypes/cogl-core-functions.h
+++ b/cogl/cogl/gl-prototypes/cogl-core-functions.h
@@ -174,6 +174,8 @@ COGL_EXT_FUNCTION (void, glTexImage2D,
                     const GLvoid* pixels))
 COGL_EXT_FUNCTION (void, glTexParameteri,
                    (GLenum target, GLenum pname, GLint param))
+COGL_EXT_FUNCTION (void, glTexParameterf,
+                   (GLenum target, GLenum pname, GLfloat param))
 COGL_EXT_FUNCTION (void, glTexParameteriv,
                    (GLenum target, GLenum pname, const GLint* params))
 COGL_EXT_FUNCTION (void, glTexSubImage2D,