OpenGL GLSL - Text rendering query

[Chebmaster]

P.S. And "untextured" coluld be a single texel stretched wide -- I adapted this strategy for my GUI to avoid unnecessary state switches.

P.P.S. Annoyingly "GL_QUADS" is deprecated and GLES doesn't have it. I went total :rageface: when I tried drawing a textured trapezoid and found that there is no good way except tesselating the tar out of it. What a bummer!
I had to recreate GL_LINE_STRIP on my own because it does not exist either. There are only triangles. Indexed ones.
On the plus side I can now use Google's "GL over Direct3d" wrapper -- ain't that neat?

[AthenaOfDelphi]

So my code does do a two pass at present and providing I use glColor4f(1.0,1.0,1.0,1.0); aka Opaque white, the blend works and the alpha is taken into account from the font texture. And everything is great, but when I change the color to say yellow, the blend changes the colour of the background quad. This is why I was looking at shaders.

Fundamentally I've been able to write a fragment shader to set the colour to a fixed value, but where I'm coming unstuck is if I use a vertex shader to extract the color (which I understand to be an interpolated value, along with the position information), I'm in a position where it breaks the 2D orthographic projection and nothing I've tried has worked. And I've tried quite a few variations of shader.

[Chebmaster]

You should not use blend, you should use alpha test.

  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
      glEnable(GL_ALPHA_TEST);
      glAlphaFunc(GL_GREATER, 0.01);

For shaders... I am beginner myself, but look at my FFP emulation for my GUI:
(please note that I calculate matrix by hand for GLES compatibility where glRotate() and the like do not exist: these are deprecated)

#version 120

uniform mat4 u_matrix;

attribute vec3 a_position;
attribute vec4 a_color;
attribute vec2 a_texCoord;

varying vec2 v_texCoord;
varying vec4 v_color;
				
void main()
{
	gl_Position = u_matrix * vec4(a_position[0], a_position[1], a_position[2], 1.0); 
	v_texCoord = a_texCoord;
	v_color = a_color;
}

#version 120

uniform sampler2D u_texture;

varying vec2 v_texCoord;
varying vec4 v_color;

void main()
{
	vec4 mytexel = texture2D( u_texture, v_texCoord);
	if (mytexel[3] < 0.05) {
		discard;
	} else {
		gl_FragColor = v_color * mytexel;
	}
}