Geometry shaders with OpenGL 2.1

[user2970139]

I am trying to use the "GL_ARB_geometry_shader4" ("GL_EXT_geometry_shader4") extension under OpenGL 2.1, GLSL 1.2 and Qt 5.3.1. After setting up the context and the format, I setup the extension:

@if (context->hasExtension(QByteArrayLiteral("GL_ARB_geometry_shader4"))) {
auto geometry_shader_ext = new QOpenGLExtension_ARB_geometry_shader4();
geometry_shader_ext->initializeOpenGLFunctions();
}@

(The extensions and the context are valid, I checked that). And then compile the shaders:

@shader_program.addShaderFromSourceFile(QOpenGLShader::Vertex,
":/shader.v.glsl");
shader_program.addShaderFromSourceFile(QOpenGLShader::Geometry,
":/shader.g.glsl");
shader_program.addShaderFromSourceFile(QOpenGLShader::Fragment,
":/shader.f.glsl");
shader_program.link();
shader_program.bind();@

With the following shader code:

@#version 120
#extension GL_ARB_geometry_shader4: enable

void main() {
vec4 p0 = gl_PositionIn[0];
vec4 p1 = gl_PositionIn[1];

...
}@

However, I get the following error:

@QOpenGLShader::compile(Geometry): ERROR: 0:17: Use of undeclared identifier 'gl_PositionIn'@

Am I missing something here?

Let me know, if you need more information.

Thanks a lot in advance.

[SGaist]

Hi,

Not really an answer but you should add which shader is generating this error.

Also, please add which combo of OS/Qt you are using

[user2970139]

The geometry shader is generating the error.

The context format:

@ QSurfaceFormat format;
format.setDepthBufferSize(24);
format.setMajorVersion(2);
format.setMinorVersion(1);
format.setSamples(4);
format.setProfile(QSurfaceFormat::CoreProfile);@

My platform: Mac OSX 10.9, NVidia 750M (I know it supports later OpenGL version, but I need to use it on older machines as well).

The shader source code:

• Vertex:

@#version 120

uniform mat4 u_pmv_matrix;

attribute vec3 a_position;
attribute vec4 a_color;
varying vec4 v_color;

void main(void) {
gl_Position = u_pmv_matrix * vec4(a_position, 1);
v_color = a_color;
}@

• Geometry

@#version 120
#extension GL_EXT_geometry_shader4: enable

uniform vec2 u_inv_viewport;
uniform float u_line_width;

varying vec4 g_color;

void main() {
vec4 p0 = gl_PositionIn[0];
vec4 p1 = gl_PositionIn[1];

vec4 dir = abs(p1 - p0);

vec2 d0 = vec2(u_line_width * p0.w) * u_inv_viewport;
vec2 d1 = vec2(u_line_width * p1.w) * u_inv_viewport;

if (dir.x > dir.y) {
d0.x = 0.0;
d1.x = 0.0;
} else {
d0.y = 0.0;
d1.y = 0.0;
}

g_color = v_color;

gl_FrontColor = gl_FrontColorIn[0];
gl_TexCoord[0] = vec4(0, 0, 0, 1);
gl_Position = p0 + vec4(d0.x, -d0.y, 0, 0);
EmitVertex();

gl_FrontColor = gl_FrontColorIn[1];
gl_TexCoord[0] = vec4(1, 0, 0, 1);
gl_Position = p1 + vec4(d1.x, -d1.y, 0, 0);
EmitVertex();

gl_FrontColor = gl_FrontColorIn[0];
gl_TexCoord[0] = vec4(0, 1, 0, 1);
gl_Position = p0 + vec4(-d0.x, d0.y, 0, 0);
EmitVertex();

gl_FrontColor = gl_FrontColorIn[1];
gl_TexCoord[0] = vec4(1, 1, 0, 1);
gl_Position = p1 + vec4(-d1.x, d1.y, 0, 0);
EmitVertex();
}@

• Fragment

@#version 120

varying vec4 g_color;

void main(void) {
gl_FragColor = g_color;
}@

[user2970139]

OpenGL context:

@Selected OpenGL version: 2.1
Context validity: 1
Used OpenGL version: 2.1
OpenGL information: VENDOR: NVIDIA Corporation
RENDERDER: NVIDIA GeForce GT 750M OpenGL Engine
VERSION: 2.1 NVIDIA-8.26.26 310.40.45f01
GLSL VERSION: 1.20
Supported extensions (139):

GL_APPLE_aux_depth_stencil
GL_APPLE_client_storage
GL_APPLE_element_array
GL_APPLE_fence
GL_APPLE_float_pixels
GL_APPLE_flush_buffer_range
GL_APPLE_flush_render
GL_APPLE_object_purgeable
GL_APPLE_packed_pixels
GL_APPLE_pixel_buffer
GL_APPLE_rgb_422
GL_APPLE_row_bytes
GL_APPLE_specular_vector
GL_APPLE_texture_range
GL_APPLE_transform_hint
GL_APPLE_vertex_array_object
GL_APPLE_vertex_array_range
GL_APPLE_vertex_point_size
GL_APPLE_vertex_program_evaluators
GL_APPLE_ycbcr_422
GL_ARB_color_buffer_float
GL_ARB_depth_buffer_float
GL_ARB_depth_clamp
GL_ARB_depth_texture
GL_ARB_draw_buffers
GL_ARB_draw_elements_base_vertex
GL_ARB_draw_instanced
GL_ARB_fragment_program
GL_ARB_fragment_program_shadow
GL_ARB_fragment_shader
GL_ARB_framebuffer_object
GL_ARB_framebuffer_sRGB
GL_ARB_half_float_pixel
GL_ARB_half_float_vertex
GL_ARB_imaging
GL_ARB_instanced_arrays
GL_ARB_multisample
GL_ARB_multitexture
GL_ARB_occlusion_query
GL_ARB_pixel_buffer_object
GL_ARB_point_parameters
GL_ARB_point_sprite
GL_ARB_provoking_vertex
GL_ARB_seamless_cube_map
GL_ARB_shader_objects
GL_ARB_shader_texture_lod
GL_ARB_shading_language_100
GL_ARB_shadow
GL_ARB_sync
GL_ARB_texture_border_clamp
GL_ARB_texture_compression
GL_ARB_texture_compression_rgtc
GL_ARB_texture_cube_map
GL_ARB_texture_env_add
GL_ARB_texture_env_combine
GL_ARB_texture_env_crossbar
GL_ARB_texture_env_dot3
GL_ARB_texture_float
GL_ARB_texture_mirrored_repeat
GL_ARB_texture_non_power_of_two
GL_ARB_texture_rectangle
GL_ARB_texture_rg
GL_ARB_transpose_matrix
GL_ARB_vertex_array_bgra
GL_ARB_vertex_blend
GL_ARB_vertex_buffer_object
GL_ARB_vertex_program
GL_ARB_vertex_shader
GL_ARB_window_pos
GL_ATI_separate_stencil
GL_ATI_texture_env_combine3
GL_ATI_texture_float
GL_ATI_texture_mirror_once
GL_EXT_abgr
GL_EXT_bgra
GL_EXT_bindable_uniform
GL_EXT_blend_color
GL_EXT_blend_equation_separate
GL_EXT_blend_func_separate
GL_EXT_blend_minmax
GL_EXT_blend_subtract
GL_EXT_clip_volume_hint
GL_EXT_debug_label
GL_EXT_debug_marker
GL_EXT_depth_bounds_test
GL_EXT_draw_buffers2
GL_EXT_draw_range_elements
GL_EXT_fog_coord
GL_EXT_framebuffer_blit
GL_EXT_framebuffer_multisample
GL_EXT_framebuffer_multisample_blit_scaled
GL_EXT_framebuffer_object
GL_EXT_framebuffer_sRGB
GL_EXT_geometry_shader4
GL_EXT_gpu_program_parameters
GL_EXT_gpu_shader4
GL_EXT_multi_draw_arrays
GL_EXT_packed_depth_stencil
GL_EXT_packed_float
GL_EXT_provoking_vertex
GL_EXT_rescale_normal
GL_EXT_secondary_color
GL_EXT_separate_specular_color
GL_EXT_shadow_funcs
GL_EXT_stencil_two_side
GL_EXT_stencil_wrap
GL_EXT_texture_array
GL_EXT_texture_compression_dxt1
GL_EXT_texture_compression_s3tc
GL_EXT_texture_env_add
GL_EXT_texture_filter_anisotropic
GL_EXT_texture_integer
GL_EXT_texture_lod_bias
GL_EXT_texture_mirror_clamp
GL_EXT_texture_rectangle
GL_EXT_texture_sRGB
GL_EXT_texture_sRGB_decode
GL_EXT_texture_shared_exponent
GL_EXT_timer_query
GL_EXT_transform_feedback
GL_EXT_vertex_array_bgra
GL_IBM_rasterpos_clip
GL_NV_blend_square
GL_NV_conditional_render
GL_NV_depth_clamp
GL_NV_fog_distance
GL_NV_fragment_program2
GL_NV_fragment_program_option
GL_NV_light_max_exponent
GL_NV_multisample_filter_hint
GL_NV_point_sprite
GL_NV_texgen_reflection
GL_NV_texture_barrier
GL_NV_vertex_program2_option
GL_NV_vertex_program3
GL_SGIS_generate_mipmap
GL_SGIS_texture_edge_clamp
GL_SGIS_texture_lod@

[user2970139]

Error log:

@QOpenGLShader::compile(Geometry): ERROR: 0:13: Use of undeclared identifier 'gl_PositionIn'
ERROR: 0:14: Use of undeclared identifier 'gl_PositionIn'
ERROR: 0:16: Use of undeclared identifier 'p1'
ERROR: 0:16: Use of undeclared identifier 'p0'
ERROR: 0:18: Use of undeclared identifier 'p0'
ERROR: 0:19: Use of undeclared identifier 'p1'
ERROR: 0:21: Use of undeclared identifier 'dir'
ERROR: 0:21: Use of undeclared identifier 'dir'
ERROR: 0:22: Use of undeclared identifier 'd0'
ERROR: 0:23: Use of undeclared identifier 'd1'
ERROR: 0:25: Use of undeclared identifier 'd0'
ERROR: 0:26: Use of undeclared identifier 'd1'
ERROR: 0:29: Use of undeclared identifier 'v_color'
ERROR: 0:31: Use of undeclared identifier 'gl_FrontColor'
ERROR: 0:31: Use of undeclared identifier 'gl_FrontColorIn'
ERROR: 0:32: Left-hand-side of assignment must not be read-only
ERROR: 0:33: Use of undeclared identifier 'gl_Position'
ERROR: 0:33: Use of undeclared identifier 'p0'
ERROR: 0:33: Use of undeclared identifier 'd0'
ERROR: 0:33: Use of undeclared identifier 'd0'
ERROR: 0:34: Call to undeclared function 'EmitVertex'
ERROR: 0:36: Use of undeclared identifier 'gl_FrontColor'
ERROR: 0:36: Use of undeclared identifier 'gl_FrontColorIn'
ERROR: 0:37: Left-hand-side of assignment must not be read-only
ERROR: 0:38: Use of undeclared identifier 'gl_Position'
ERROR: 0:38: Use of undeclared identifier 'p1'
ERROR: 0:38: Use of undeclared identifier 'd1'
ERROR: 0:38: Use of undeclared identifier 'd1'
ERROR: 0:39: Call to undeclared function 'EmitVertex'
ERROR: 0:41: Use of undeclared identifier 'gl_FrontColor'
ERROR: 0:41: Use of undeclared identifier 'gl_FrontColorIn'
ERROR: 0:42: Left-hand-side of assignment must not be read-only
ERROR: 0:43: Use of undeclared identifier 'gl_Position'
ERROR: 0:43: Use of undeclared identifier 'p0'
ERROR: 0:43: Use of undeclared identifier 'd0'
ERROR: 0:43: Use of undeclared identifier 'd0'
ERROR: 0:44: Call to undeclared function 'EmitVertex'
ERROR: 0:46: Use of undeclared identifier 'gl_FrontColor'
ERROR: 0:46: Use of undeclared identifier 'gl_FrontColorIn'
ERROR: 0:47: Left-hand-side of assignment must not be read-only
ERROR: 0:48: Use of undeclared identifier 'gl_Position'
ERROR: 0:48: Use of undeclared identifier 'p1'
ERROR: 0:48: Use of undeclared identifier 'd1'
ERROR: 0:48: Use of undeclared identifier 'd1'
ERROR: 0:49: Call to undeclared function 'EmitVertex'

*** Problematic Geometry shader source code ***
#version 120
#extension GL_EXT_geometry_shader4: enable
#define lowp
#define mediump
#define highp

uniform vec2 u_inv_viewport;
uniform float u_line_width;

varying vec4 g_color;

void main() {
vec4 p0 = gl_PositionIn[0];
vec4 p1 = gl_PositionIn[1];

vec4 dir = abs(p1 - p0);

vec2 d0 = vec2(u_line_width * p0.w) * u_inv_viewport;
vec2 d1 = vec2(u_line_width * p1.w) * u_inv_viewport;

if (dir.x > dir.y) {
d0.x = 0.0;
d1.x = 0.0;
} else {
d0.y = 0.0;
d1.y = 0.0;
}

g_color = v_color;

gl_FrontColor = gl_FrontColorIn[0];
gl_TexCoord[0] = vec4(0, 0, 0, 1);
gl_Position = p0 + vec4(d0.x, -d0.y, 0, 0);
EmitVertex();

gl_FrontColor = gl_FrontColorIn[1];
gl_TexCoord[0] = vec4(1, 0, 0, 1);
gl_Position = p1 + vec4(d1.x, -d1.y, 0, 0);
EmitVertex();

gl_FrontColor = gl_FrontColorIn[0];
gl_TexCoord[0] = vec4(0, 1, 0, 1);
gl_Position = p0 + vec4(-d0.x, d0.y, 0, 0);
EmitVertex();

gl_FrontColor = gl_FrontColorIn[1];
gl_TexCoord[0] = vec4(1, 1, 0, 1);
gl_Position = p1 + vec4(-d1.x, d1.y, 0, 0);
EmitVertex();
}

---

QOpenGLShader::link: "WARNING: Output of vertex shader 'v_color' not read by fragment shader
ERROR: Input of fragment shader 'g_color' not written by vertex shader
"
QOpenGLShader::link: "WARNING: Output of vertex shader 'v_color' not read by fragment shader
ERROR: Input of fragment shader 'g_color' not written by vertex shader
"
@