Re: GL_ACTIVE_UNIFORMS returns unexpected value

On 03/19/2015 08:20 AM, Brian Paul wrote:
> On 03/19/2015 04:16 AM, Lascha Lagidse wrote:
>> On 3/18/2015 6:12 PM, Brian Paul wrote:
>>> On 03/18/2015 09:37 AM, Lascha Lagidse wrote:
>>>> Hello :)
>>>>
>>>> I am Lascha, new to linux and first time subscribing to a mailing list.
>>>> I heard you were great guys ;)
>>>
>>> We try to be. :)
>>>
>>>
>>>> So, I am currently in the process of porting the game Age of Wonders 3
>>>> to Linux. The game is currently in open-beta on Steam, and people
>>>> reported issues with the specifically the Mesa graphics driver. I had a
>>>> look and it looks like this driver behaves differently on this driver
>>>> when using glGetProgramiv and glGetActiveUniform.
>>>>
>>>> The vertex shader (see bottom) is attached to a program. The program is
>>>> then linked. Note: Only this vertex shader is attached to the program;
>>>> there is no other shader attached. Now using glGetProgramiv with
>>>> GL_ACTIVE_UNIFORMS will return 2, but I expect it to be 3 like on the
>>>> other drivers. According to glGetActiveUniform it is the variable 'c24'
>>>> which is missing. My guess is that it's optimized away, for some
>>>> reason.
>>>> If I also link the fragment shader, then 'c24' is listed correctly.
>>>>
>>>> My goal is to retrieve the active uniforms from specifically the vertex
>>>> shader. If I link both the vertex AND the fragment program, then there
>>>> is no way to distinguish which uniforms belong to the vertex program
>>>> and
>>>> which belong to the fragment program (or is there?).
>>>>
>>>> I can't think of a nice work-around; but since this is only
>>>> initialization code the only work-around that comes to mind is to
>>>> serialize the info I get from glGetActiveUniform on another driver and
>>>> use that info instead of calling glGetActiveUniform at initialization.
>>>>
>>>> #version 140
>>>> uniform mat4 c20;
>>>> uniform vec4 c24;
>>>> uniform vec4 c25;
>>>> in vec3 POSITION0;
>>>> in vec2 TEXCOORD0;
>>>> out vec2 xlv_TEXCOORD0;
>>>> void main ()
>>>> {
>>>>    vec4 PosWS_1;
>>>>    PosWS_1.xy = (c25.xy + (POSITION0.xy * c25.zw));
>>>>    PosWS_1.z = POSITION0.z;
>>>>    PosWS_1.w = 1.0;
>>>>    gl_Position = (c20 * PosWS_1);
>>>>    xlv_TEXCOORD0 = (c24.xy + (TEXCOORD0 * c24.zw));
>>>> }
>>>
>>> Which version of Mesa are you using?  Would it be possible to get a
>>> simple glut/piglit test program?
>>>
>>> -Brian
>>>
>> Sorry if you're receiving this multiple times. I think I should have
>> used 'Reply All' instead of 'Reply'. Realized this too late.
>>
>> I'm using "3.3 (Core profile) Mesa 10.3.2" (according to GL_VERSION).
>>
>> Here is a simple test program. It uses freeglut and glew. I hope that's
>> okay.
>>
>> #include <GL/glew.h>
>> #include <GL/freeglut.h>
>> #include <stdlib.h>
>> #include <cstdio>
>> #include <cstring>
>>
>> int main(int argc, char *argv[])
>> {
>>    glutInit(&argc, argv);
>>    glutInitWindowSize(128,128);
>>    glutInitWindowPosition(10,10);
>>    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
>>    glutInitContextVersion(3, 3);
>>    glutInitContextFlags(GLUT_CORE_PROFILE);
>>    glutCreateWindow("LinuxShaderBug");
>>    glewInit();
>>
>>    printf("version: %s\n", glGetString(GL_VERSION));
>>
>>    const GLchar* shader_code = "#version 140\n\
>>      uniform mat4 c20;\n\
>>      uniform vec4 c24;\n\
>>      uniform vec4 c25;\n\
>>      in vec3 POSITION0;\n\
>>      in vec2 TEXCOORD0;\n\
>>      out vec2 xlv_TEXCOORD0;\n\
>>      void main ()\n\
>>      {\n\
>>        vec4 PosWS_1;\n\
>>        PosWS_1.xy = (c25.xy + (POSITION0.xy * c25.zw));\n\
>>        PosWS_1.z = POSITION0.z;\n\
>>        PosWS_1.w = 1.0;\n\
>>        gl_Position = (c20 * PosWS_1);\n\
>>        xlv_TEXCOORD0 = (c24.xy + (TEXCOORD0 * c24.zw));\n\
>>      }\n";
>>
>>    const GLchar* shader_code_array[1] = { shader_code };
>>    const GLint shader_size_array[1] = { strlen(shader_code) };
>>    GLuint shader_handle = glCreateShader(GL_VERTEX_SHADER);
>>    glShaderSource(shader_handle, 1, shader_code_array,
>> shader_size_array);
>>    glCompileShader(shader_handle);
>>
>>    GLuint program_handle = glCreateProgram();
>>    glAttachShader(program_handle, shader_handle);
>>    glLinkProgram(program_handle);
>>
>>    GLint num_uniforms = 0;
>>    glGetProgramiv(program_handle, GL_ACTIVE_UNIFORMS, &num_uniforms);
>>    printf("num_uniforms: %i\n", num_uniforms);
>>
>>    char u_name[32];
>>    GLsizei u_name_len = 0;
>>    GLint u_size = 0;
>>    GLenum u_type = GL_NONE;
>>    GLint u_idx = 0;
>>
>>    for (u_idx = 0; u_idx < num_uniforms; ++u_idx)
>>    {
>>      glGetActiveUniform(program_handle, u_idx, 31, &u_name_len, &u_size,
>> &u_type, &u_name[0]);
>>      printf("u_name: %s\n", u_name);
>>    }
>>
>>    return EXIT_SUCCESS;
>> }
>
> Thanks.  Looks like it's the same with current Mesa from git.  Seems
> like a bug to me.  I'll probably convert your test to a piglit test. Not
> sure if I'll have time to debug this, bug I can file a bug anyway.

Actually, this may not be a bug.  Since there's no fragment shader, the 
xlv_TEXCOORD0 output variable is unused.  Therefore, the uniform c24 is 
unused also.  So that's why it's not considered active.

Does your actual program have a fragment shader that uses xlv_TEXCOORD0?

-Brian


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