OpenGL ES 3.0 GL_POINTS doesn't render anything - linux

Question

Below is a mininal reproducer:
GL_CHECK(glClearColor(0.4f, 0.4f, 0.4f, 1.0f));
GL_CHECK(glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT |
GL_STENCIL_BUFFER_BIT));
GL_CHECK(glUseProgram(this->pp_->shader_program));
GL_CHECK(glEnable(GL_TEXTURE_2D));
GL_CHECK(glActiveTexture(GL_TEXTURE0));
GL_CHECK(glBindTexture(GL_TEXTURE_2D, this->particle_->id));
GLfloat points[] = { 150.f, 150.f, 10.0f, 150.0f, 175.0f, 10.0f };
GLfloat colors[] = { 1.0f, 0.0f, 0.0f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f };
shader_pass_set_uniform(this->pp_, HASH("mvp"), glm::value_ptr(this->camera_));
GL_CHECK(glEnableVertexAttribArray(0));
GL_CHECK(glEnableVertexAttribArray(3));
GL_CHECK(glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, &points[0]));
GL_CHECK(glVertexAttribPointer(3, 4, GL_FLOAT, GL_FALSE, 0, &colors[0]));
GL_CHECK(glDrawArrays(GL_POINTS, 0, 2));
vertex shader:
#version 300 es
layout(location = 0) in highp vec3 vertex;
layout(location = 3) in highp vec4 color;
out lowp vec4 vcolor;
uniform mat4 mvp;
void main()
{
vcolor = color;
gl_Position = mvp * vec4(vertex.xy, 0.0, 1.0);
gl_PointSize = vertex.z;
}
fragment shader:
#version 300 es
uniform sampler2D stexture;
in lowp vec4 vcolor;
layout(location = 0) out lowp vec4 ocolor;
void main()
{
ocolor = texture(stexture, gl_PointCoord) * vcolor;
}
Nothing gets rendered on-screen, my glxinfo can be found in this pastebin. When I render the same texture onto a triangle it works.
Here is also the render loop as captured with apitrace:
250155 glClearColor(red = 0.5, green = 0.5, blue = 0.5, alpha = 1)
250157 glClear(mask = GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT | GL_COLOR_BUFFER_BIT)
250159 glUseProgram(program = 9)
250161 glEnable(cap = GL_TEXTURE_2D)
250163 glActiveTexture(texture = GL_TEXTURE0)
250165 glBindTexture(target = GL_TEXTURE_2D, texture = 2)
250167 glUniformMatrix4fv(location = 0, count = 1, transpose = GL_FALSE, value = {0.001953125, 0, 0, 0, 0, 0.002604167, 0, 0, 0, 0, -1, 0, -1, -1, -0, 1})
250168 glEnableVertexAttribArray(index = 0)
250170 glEnableVertexAttribArray(index = 3)
250174 glVertexAttribPointer(index = 0, size = 3, type = GL_FLOAT, normalized = GL_FALSE, stride = 0, pointer = blob(24))
250175 glVertexAttribPointer(index = 3, size = 4, type = GL_FLOAT, normalized = GL_FALSE, stride = 0, pointer = blob(32))
250176 glDrawArrays(mode = GL_POINTS, first = 0, count = 2)
250178 glXSwapBuffers(dpy = 0x1564010, drawable = 50331661)

Answer 1

I guess that could mean, that the range of point sizes, that your GLES implementation supports, may be not what you are expecting. You can try something like:
GLint range[2];
glGetIntegerv(GL_ALIASED_POINT_SIZE_RANGE, range); // for example, (1, 511) in my implementation
to check it out. Any implementation guarantees, that range[1] is at least 1.0. The value gl_PointSize is getting clamped to the range, so in the worst case you won't be able to set point with size, greater than 1. In this case gl_PointCoord seems to evaluate to (1, 0) (according to formula from specs) at the only fragment, that is going to be drawn for each point. After the texture's wrap mode come into play, (1, 0) may turn into (0, 0), for example if you are using GL_REPEAT as the texture's wrap mode. If you'd like to safely draw a point with side, greater than one, you should try using the ordinary way to draw squares (for example using four vertices and GL_TRIANGLE_FAN or GL_TRIANGLE_STRIP mode).