Fixing wierd edges with transparent billboarded particles

BillboardingParticles.cpp

void GlowiesManager::draw(const Mat4& pm, const Mat4& vm, const Vec3& right, const Vec3& up) {
	glEnable(GL_BLEND);
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

	// IMPORTANT: disable depth mask writing to prevent wierd looking edges while  using transparency!
	// ------------------------------------------------------------------------------------------------
	glDepthMask(GL_FALSE);
	
	for(vector<GlowiesData>::iterator git = collections.begin(); git != collections.end(); ++git) {
		GlowiesData& gd = (*git);
		Glowies& gl = *gd.glowies;
		
		
		glBindVertexArrayAPPLE(gd.vao); eglGetError();

		gd.shader->enable();
		gd.shader->uniformMat4fv("u_projection_matrix", pm.getPtr());
		gd.shader->uniformMat4fv("u_view_matrix", vm.getPtr());

		// set texture.
		glActiveTexture(GL_TEXTURE2);
		glBindTexture(GL_TEXTURE_2D, gd.tex);
		gd.shader->uniform1i("u_texture", 2);

		for(vector<Particle*>::iterator pit = ps.particles.begin(); pit != ps.particles.end(); ++pit) {
			Particle& p = *(*pit);
			gl.position = p.position;
			gl.sort();
			for(vector<Glowy>::iterator glit = gl.glowies.begin(); glit != gl.glowies.end(); ++glit) {
				Glowy& glowy = (*glit);
				
				Mat4 model_matrix;
				model_matrix.setBillboard(right, up);
				model_matrix.setPosition(glowy.position);
				model_matrix.scale(glowy.radius);
				
				Quat q;
				q.rotate(glowy.rotation * DEG_TO_RAD,0,0,1);
				model_matrix = model_matrix * q.getMat4();
				
				gd.shader->uniform1f("u_alpha", glowy.agep);
				
			
				gd.shader->uniformMat4fv("u_model_matrix", model_matrix.getPtr());
				glDrawArrays(GL_QUADS, 0, 4);
			}
		}
		
		gd.shader->disable();
		glBindVertexArrayAPPLE(0); eglGetError();		
	}	
	glDepthMask(GL_TRUE);
}

Result w/o disabling depth mask:

Result with disabling depth mask.

Using particle image: