vo_opengl: don't use 10 bit video on Intel GPUs

vo_opengl was originally written against OpenGL 3 core, and it seems
GPUs/drivers supporting this are mostly sane. Later, it was made to work
with OpenGL 2.1 too. Lately we removed the requirement for RG textures,
and look, someone reported a problem with "lesser" Intel GPUs.

This commit does the same in vo_opengl what was added to vo_opengl_old a
long time ago.

Fixes #1383.

Conflicts:
	video/out/gl_common.c
	video/out/gl_video.c

2 files changed, 31 insertions, 0 deletions

diff --git a/video/out/gl_common.c b/video/out/gl_common.c
index 1a966224a2..d90dd57d5e 100644
--- a/video/out/gl_common.c
+++ b/video/out/gl_common.c
@@ -265,6 +265,7 @@ static const struct gl_functions gl_functions[] = {
         .provides = MPGL_CAP_GL3 | MPGL_CAP_SRGB_TEX | MPGL_CAP_SRGB_FB,
         .functions = (const struct gl_function[]) {
             DEF_FN(GetStringi),
+            DEF_FN(GetTexLevelParameteriv),
             {0}
         },
     },
diff --git a/video/out/gl_video.c b/video/out/gl_video.c
index 8cd302e7b8..f4cdff3c5c 100644
--- a/video/out/gl_video.c
+++ b/video/out/gl_video.c
@@ -146,6 +146,7 @@ struct gl_video {
     bool gl_debug;
 
     int depth_g;
+    int texture_16bit_depth;    // actual bits available in 16 bit textures
 
     GLenum gl_target; // texture target (GL_TEXTURE_2D, ...) for video and FBOs
 
@@ -2199,6 +2200,29 @@ static int init_gl(struct gl_video *p)
 
     gl->ClearColor(0.0f, 0.0f, 0.0f, 1.0f);
 
+    // Test whether we can use 10 bit. Hope that testing a single format/channel
+    // is good enough (instead of testing all 1-4 channels variants etc.).
+    const struct fmt_entry *fmt = find_tex_format(gl, 2, 1);
+    if (gl->GetTexLevelParameteriv && fmt->format) {
+        GLuint tex;
+        gl->GenTextures(1, &tex);
+        gl->BindTexture(GL_TEXTURE_2D, tex);
+        gl->TexImage2D(GL_TEXTURE_2D, 0, fmt->internal_format, 64, 64, 0,
+                       fmt->format, fmt->type, NULL);
+        GLenum pname = 0;
+        switch (fmt->format) {
+        case GL_RED:        pname = GL_TEXTURE_RED_SIZE; break;
+        case GL_LUMINANCE:  pname = GL_TEXTURE_LUMINANCE_SIZE; break;
+        }
+        GLint param = 0;
+        if (pname)
+            gl->GetTexLevelParameteriv(GL_TEXTURE_2D, 0, pname, &param);
+        if (param) {
+            MP_VERBOSE(p, "16 bit texture depth: %d.\n", (int)param);
+            p->texture_16bit_depth = param;
+        }
+    }
+
     debug_check_gl(p, "after init_gl");
 
     return 1;
@@ -2343,6 +2367,11 @@ supported:
     if (desc.num_planes == 4 && (init->plane_bits % 8) != 0)
         return false;
 
+    if (init->plane_bits > 8 && init->plane_bits < 16) {
+        if (init->texture_16bit_depth < 16)
+            return false;
+    }
+
     for (int p = 0; p < desc.num_planes; p++) {
         struct texplane *plane = &init->image.planes[p];
         const struct fmt_entry *format = plane_format[p];
@@ -2396,6 +2425,7 @@ struct gl_video *gl_video_init(GL *gl, struct mp_log *log, struct osd_state *osd
         .opts = gl_video_opts_def,
         .gl_target = GL_TEXTURE_2D,
         .gl_debug = true,
+        .texture_16bit_depth = 16,
         .scalers = {
             { .index = 0, .name = "bilinear" },
             { .index = 1, .name = "bilinear" },