[Mesa-dev] [PATCH 2/5] meta: fix meta clear of layered framebuffers

[Marek Olšák]

I currently work on a simpler solution for Gallium. I'm using
AMD_vertex_shader_layer and this vertex shader (I wrote it in TGSI
though):

void main()
{
    gl_Position = gl_Vertex;
    gl_TexCoord[0] = MultiTexCoord0; // clear color
    gl_Layer = gl_InstanceID;
}

Then I render the quad with DrawArraysInstanced and set the instance
count = NumLayers. That way each instance (each quad) is sent to a
different layer and everything is cleared in one draw call.

Drivers not supporting AMD_vertex_shader_layer will have to use a GS though.

Marek


On Wed, Nov 20, 2013 at 5:47 AM, Paul Berry <stereotype441 at gmail.com> wrote:
> From section 4.4.7 (Layered Framebuffers) of the GLSL 3.2 spec:
>
>     When the Clear or ClearBuffer* commands are used to clear a
>     layered framebuffer attachment, all layers of the attachment are
>     cleared.
>
> This patch fixes meta clears to properly clear all layers of a layered
> framebuffer attachment.  We accomplish this by adding a geometry
> shader to the meta clear program which sets gl_Layer to a uniform
> value.  When clearing a layered framebuffer, we execute in a loop,
> setting the uniform to point to each layer in turn.
>
> Cc: "10.0" <mesa-stable at lists.freedesktop.org>
> ---
>  src/mesa/drivers/common/meta.c | 51 +++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 48 insertions(+), 3 deletions(-)
>
> diff --git a/src/mesa/drivers/common/meta.c b/src/mesa/drivers/common/meta.c
> index 99b02ba..a6d5098 100644
> --- a/src/mesa/drivers/common/meta.c
> +++ b/src/mesa/drivers/common/meta.c
> @@ -241,9 +241,11 @@ struct clear_state
>     GLuint VBO;
>     GLuint ShaderProg;
>     GLint ColorLocation;
> +   GLint LayerLocation;
>
>     GLuint IntegerShaderProg;
>     GLint IntegerColorLocation;
> +   GLint IntegerLayerLocation;
>  };
>
>
> @@ -2145,6 +2147,19 @@ meta_glsl_clear_init(struct gl_context *ctx, struct clear_state *clear)
>        "{\n"
>        "   gl_Position = position;\n"
>        "}\n";
> +   const char *gs_source =
> +      "#version 150\n"
> +      "layout(triangles) in;\n"
> +      "layout(triangle_strip, max_vertices = 4) out;\n"
> +      "uniform int layer;\n"
> +      "void main()\n"
> +      "{\n"
> +      "  for (int i = 0; i < 3; i++) {\n"
> +      "    gl_Layer = layer;\n"
> +      "    gl_Position = gl_in[i].gl_Position;\n"
> +      "    EmitVertex();\n"
> +      "  }\n"
> +      "}\n";
>     const char *fs_source =
>        "#ifdef GL_ES\n"
>        "precision highp float;\n"
> @@ -2154,7 +2169,7 @@ meta_glsl_clear_init(struct gl_context *ctx, struct clear_state *clear)
>        "{\n"
>        "   gl_FragColor = color;\n"
>        "}\n";
> -   GLuint vs, fs;
> +   GLuint vs, gs = 0, fs;
>     bool has_integer_textures;
>
>     if (clear->ArrayObj != 0)
> @@ -2176,6 +2191,12 @@ meta_glsl_clear_init(struct gl_context *ctx, struct clear_state *clear)
>     _mesa_ShaderSource(vs, 1, &vs_source, NULL);
>     _mesa_CompileShader(vs);
>
> +   if (_mesa_has_geometry_shaders(ctx)) {
> +      gs = _mesa_CreateShaderObjectARB(GL_GEOMETRY_SHADER);
> +      _mesa_ShaderSource(gs, 1, &gs_source, NULL);
> +      _mesa_CompileShader(gs);
> +   }
> +
>     fs = _mesa_CreateShaderObjectARB(GL_FRAGMENT_SHADER);
>     _mesa_ShaderSource(fs, 1, &fs_source, NULL);
>     _mesa_CompileShader(fs);
> @@ -2183,6 +2204,8 @@ meta_glsl_clear_init(struct gl_context *ctx, struct clear_state *clear)
>     clear->ShaderProg = _mesa_CreateProgramObjectARB();
>     _mesa_AttachShader(clear->ShaderProg, fs);
>     _mesa_DeleteObjectARB(fs);
> +   if (gs != 0)
> +      _mesa_AttachShader(clear->ShaderProg, gs);
>     _mesa_AttachShader(clear->ShaderProg, vs);
>     _mesa_DeleteObjectARB(vs);
>     _mesa_BindAttribLocation(clear->ShaderProg, 0, "position");
> @@ -2190,6 +2213,10 @@ meta_glsl_clear_init(struct gl_context *ctx, struct clear_state *clear)
>
>     clear->ColorLocation = _mesa_GetUniformLocation(clear->ShaderProg,
>                                                       "color");
> +   if (gs != 0) {
> +      clear->LayerLocation = _mesa_GetUniformLocation(clear->ShaderProg,
> +                                                     "layer");
> +   }
>
>     has_integer_textures = _mesa_is_gles3(ctx) ||
>        (_mesa_is_desktop_gl(ctx) && ctx->Const.GLSLVersion >= 130);
> @@ -2227,6 +2254,8 @@ meta_glsl_clear_init(struct gl_context *ctx, struct clear_state *clear)
>        clear->IntegerShaderProg = _mesa_CreateProgramObjectARB();
>        _mesa_AttachShader(clear->IntegerShaderProg, fs);
>        _mesa_DeleteObjectARB(fs);
> +      if (gs != 0)
> +         _mesa_AttachShader(clear->IntegerShaderProg, gs);
>        _mesa_AttachShader(clear->IntegerShaderProg, vs);
>        _mesa_DeleteObjectARB(vs);
>        _mesa_BindAttribLocation(clear->IntegerShaderProg, 0, "position");
> @@ -2240,7 +2269,13 @@ meta_glsl_clear_init(struct gl_context *ctx, struct clear_state *clear)
>
>        clear->IntegerColorLocation =
>          _mesa_GetUniformLocation(clear->IntegerShaderProg, "color");
> +      if (gs != 0) {
> +         clear->IntegerLayerLocation =
> +            _mesa_GetUniformLocation(clear->IntegerShaderProg, "layer");
> +      }
>     }
> +   if (gs != 0)
> +      _mesa_DeleteObjectARB(gs);
>  }
>
>  static void
> @@ -2371,8 +2406,18 @@ _mesa_meta_glsl_Clear(struct gl_context *ctx, GLbitfield buffers)
>     _mesa_BufferData(GL_ARRAY_BUFFER_ARB, sizeof(verts), verts,
>                        GL_DYNAMIC_DRAW_ARB);
>
> -   /* draw quad */
> -   _mesa_DrawArrays(GL_TRIANGLE_FAN, 0, 4);
> +   /* draw quad(s) */
> +   if (fb->Layered) {
> +      for (unsigned layer = 0; layer < fb->NumLayers; layer++) {
> +         if (fb->_IntegerColor)
> +            _mesa_Uniform1i(clear->IntegerLayerLocation, layer);
> +         else
> +            _mesa_Uniform1i(clear->LayerLocation, layer);
> +         _mesa_DrawArrays(GL_TRIANGLE_FAN, 0, 4);
> +      }
> +   } else {
> +      _mesa_DrawArrays(GL_TRIANGLE_FAN, 0, 4);
> +   }
>
>     _mesa_meta_end(ctx);
>  }
> --
> 1.8.4.2
>
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