vo_opengl: enable compute shader for mesa

Mesa 17.1 supports compute shader but not full specs of OpenGL 4.3.
Change the code to detect OpenGL extension "GL_ARB_compute_shader"
rather than OpenGL version 4.3.

HDR peak detection requires SSBO, and polar scaler requires 2D array
extension. Add these extensions as requirement as well.

5 files changed, 26 insertions, 4 deletions

diff --git a/video/out/opengl/common.c b/video/out/opengl/common.c
index 9af21856ab..c7a714817a 100644
--- a/video/out/opengl/common.c
+++ b/video/out/opengl/common.c
@@ -357,6 +357,11 @@ static const struct gl_functions gl_functions[] = {
             {0},
         },
     },
+    {
+        .ver_core = 430,
+        .extension = "GL_ARB_arrays_of_arrays",
+        .provides = MPGL_CAP_NESTED_ARRAY,
+    },
     // Swap control, always an OS specific extension
     // The OSX code loads this manually.
     {
@@ -619,6 +624,10 @@ void mpgl_load_functions2(GL *gl, void *(*get_fn)(void *ctx, const char *n),
         mp_verbose(log, "Detected suspected software renderer.\n");
     }
 
+    // GL_ARB_compute_shader & GL_ARB_shader_image_load_store
+    if (gl->DispatchCompute && gl->BindImageTexture)
+        gl->mpgl_caps |= MPGL_CAP_COMPUTE_SHADER;
+
     // Provided for simpler handling if no framebuffer support is available.
     if (!gl->BindFramebuffer)
         gl->BindFramebuffer = &dummy_glBindFramebuffer;
diff --git a/video/out/opengl/common.h b/video/out/opengl/common.h
index eec7806624..6d8015c8b3 100644
--- a/video/out/opengl/common.h
+++ b/video/out/opengl/common.h
@@ -55,6 +55,8 @@ enum {
     MPGL_CAP_ARB_FLOAT          = (1 << 19),    // GL_ARB_texture_float
     MPGL_CAP_EXT_CR_HFLOAT      = (1 << 20),    // GL_EXT_color_buffer_half_float
     MPGL_CAP_SSBO               = (1 << 21),    // GL_ARB_shader_storage_buffer_object
+    MPGL_CAP_COMPUTE_SHADER     = (1 << 22),    // GL_ARB_compute_shader & GL_ARB_shader_image_load_store
+    MPGL_CAP_NESTED_ARRAY       = (1 << 23),    // GL_ARB_arrays_of_arrays
 
     MPGL_CAP_SW                 = (1 << 30),    // indirect or sw renderer
 };
diff --git a/video/out/opengl/utils.c b/video/out/opengl/utils.c
index afbd6f65af..451010fffa 100644
--- a/video/out/opengl/utils.c
+++ b/video/out/opengl/utils.c
@@ -777,6 +777,8 @@ void gl_sc_uniform_image2D(struct gl_shader_cache *sc, char *name, GLuint textur
 void gl_sc_ssbo(struct gl_shader_cache *sc, char *name, GLuint ssbo,
                 char *format, ...)
 {
+    gl_sc_enable_extension(sc, "GL_ARB_shader_storage_buffer_object");
+
     struct sc_buffer *b = find_buffer(sc, name);
     b->binding = sc->next_buffer_binding++;
     b->ssbo = ssbo;
@@ -1179,6 +1181,11 @@ struct mp_pass_perf gl_sc_generate(struct gl_shader_cache *sc, GLenum type)
     // set up shader text (header + uniforms + body)
     bstr *header = &sc->tmp[0];
     ADD(header, "#version %d%s\n", gl->glsl_version, gl->es >= 300 ? " es" : "");
+    if (type == GL_COMPUTE_SHADER) {
+        // This extension cannot be enabled in fragment shader. Enable it as
+        // an exception for compute shader.
+        ADD(header, "#extension GL_ARB_compute_shader : enable\n");
+    }
     for (int n = 0; n < sc->num_exts; n++)
         ADD(header, "#extension %s : enable\n", sc->exts[n]);
     if (gl->es) {
diff --git a/video/out/opengl/video.c b/video/out/opengl/video.c
index d4f746e3a2..e1fd60646a 100644
--- a/video/out/opengl/video.c
+++ b/video/out/opengl/video.c
@@ -1183,7 +1183,7 @@ static void dispatch_compute(struct gl_video *p, int w, int h, int bw, int bh)
         // Clamp the texture coordinates to prevent sampling out-of-bounds in
         // threads that exceed the requested width/height
         PRELUDE("#define texmap%d(id) min(texcoord%d_rot(id), vec2(1.0))\n", n, n);
-        PRELUDE("const vec2 texcoord%d = texmap%d(gl_GlobalInvocationID);\n", n, n);
+        PRELUDE("vec2 texcoord%d = texmap%d(gl_GlobalInvocationID);\n", n, n);
     }
 
     pass_record(p, gl_sc_generate(p->sc, GL_COMPUTE_SHADER));
@@ -1756,10 +1756,12 @@ static void pass_sample(struct gl_video *p, struct img_tex tex,
     } else if (strcmp(name, "oversample") == 0) {
         pass_sample_oversample(p->sc, scaler, w, h);
     } else if (scaler->kernel && scaler->kernel->polar) {
+        bool use_compute_polar = (p->gl->mpgl_caps & MPGL_CAP_COMPUTE_SHADER) &&
+                                 (p->gl->mpgl_caps & MPGL_CAP_NESTED_ARRAY);
         // Use a compute shader where possible, fallback to the slower texture
         // fragment sampler otherwise. Also use the fragment shader for
         // very large kernels to avoid exhausting shmem
-        if (p->gl->glsl_version < 430 || scaler->kernel->f.radius > 16) {
+        if (!use_compute_polar || scaler->kernel->f.radius > 16) {
             pass_sample_polar(p->sc, scaler, tex.components, p->gl->glsl_version);
         } else {
             // For performance we want to load at least as many pixels
@@ -3391,7 +3393,8 @@ static void check_gl_features(struct gl_video *p)
     bool have_mglsl = gl->glsl_version >= 130; // modern GLSL (1st class arrays etc.)
     bool have_texrg = gl->mpgl_caps & MPGL_CAP_TEX_RG;
     bool have_tex16 = !gl->es || (gl->mpgl_caps & MPGL_CAP_EXT16);
-    bool have_compute = gl->glsl_version >= 430; // easiest way to ensure all
+    bool have_compute = gl->mpgl_caps & MPGL_CAP_COMPUTE_SHADER;
+    bool have_ssbo = gl->mpgl_caps & MPGL_CAP_SSBO;
 
     const GLint auto_fbo_fmts[] = {GL_RGBA16, GL_RGBA16F, GL_RGB10_A2,
                                    GL_RGBA8, 0};
@@ -3502,7 +3505,7 @@ static void check_gl_features(struct gl_video *p)
         p->opts.deband = 0;
         MP_WARN(p, "Disabling debanding (GLSL version too old).\n");
     }
-    if (!have_compute && p->opts.compute_hdr_peak) {
+    if ((!have_compute || !have_ssbo) && p->opts.compute_hdr_peak) {
         p->opts.compute_hdr_peak = 0;
         MP_WARN(p, "Disabling HDR peak computation (no compute shaders).\n");
     }
diff --git a/video/out/opengl/video_shaders.c b/video/out/opengl/video_shaders.c
index fe6e944168..854c829f1d 100644
--- a/video/out/opengl/video_shaders.c
+++ b/video/out/opengl/video_shaders.c
@@ -241,6 +241,7 @@ void pass_compute_polar(struct gl_shader_cache *sc, struct scaler *scaler,
     gl_sc_uniform_tex(sc, "lut", scaler->gl_target, scaler->gl_lut);
 
     // Load all relevant texels into shmem
+    gl_sc_enable_extension(sc, "GL_ARB_arrays_of_arrays");
     for (int c = 0; c < components; c++)
         GLSLHF("shared float in%d[%d][%d];\n", c, ih, iw);