Example using texture internalformat for higher precision

Generates a gradient texture with high dynamic range and renders it with a fragment shader that tests for quantization errors by comparing adjacent texels and decomposes the gradient values into high and low significance bits, mapping them to separate display color channels.

Pressing the ‘f’ key cycles through a list of different texture formats to show the different levels of precision available.

Requesting texture internalformat rgb8

import numpy as np
from vispy import gloo
from vispy import app

W, H = 1024, 1024

# prepare a gradient field with high dynamic range
data = np.zeros((H, W, 3), np.float32)

for i in range(W):
    data[:, i, :] = i**2

for i in range(H):
    data[i, :, :] *= i**2

data *= 1./data.max()

# prepare a simple quad to cover the viewport
quad = np.zeros(4, dtype=[
    ('a_position', np.float32, 2),
    ('a_texcoord', np.float32, 2)
])

quad['a_position'] = np.array([[-1, -1], [+1, -1], [-1, +1], [+1, +1]])
quad['a_texcoord'] = np.array([[0, 0], [1, 0], [0, 1], [1, 1]])

vert_shader = """
attribute vec2 a_position;
attribute vec2 a_texcoord;
varying vec2 v_texcoord;

void main()
{
   v_texcoord = a_texcoord;
   gl_Position = vec4(a_position, 0.0, 1.0);
}
"""

frag_shader = """
uniform sampler2D u_texture;
varying vec2 v_texcoord;

void main()
{
   float ndiff;
   // an adjacent texel is 1/W further over in normalized texture coordinates
   vec2 v_texcoord2 = vec2(clamp(v_texcoord.x + 1.0/%(W)d., 0.0, 1.0),
                           v_texcoord.y);
   vec4 texel1 = texture2D(u_texture, v_texcoord);
   vec4 texel2 = texture2D(u_texture, v_texcoord2);

   // test for quantized binning of adjacent texels
   if (texel1.r == texel2.r && v_texcoord2.x < 1.0 && v_texcoord.y > 0.0)
      ndiff = 1.0;
   else
      ndiff = 0.0;

   gl_FragColor = vec4(
      fract(texel1.r * 255.0),  // render low-significance bits as red
      texel1.r,                 // render high-significance bits as green
      ndiff,                    // flag quantized bands as blue
      1);
}
""" % dict(W=W)


class Canvas(app.Canvas):

    def __init__(self):
        app.Canvas.__init__(self, size=(W, H), keys='interactive')

        self._internalformats = [
            'rgb8',
            'rgb16',
            'rgb16f',
            'rgb32f'
        ]

        self.program = gloo.Program(vert_shader, frag_shader)
        self.program.bind(gloo.VertexBuffer(quad))
        self._internalformat = -1
        self.texture = gloo.Texture2D(
            shape=(H, W, 3),
            interpolation='nearest'
        )

        gloo.set_viewport(0, 0, *self.physical_size)

        self.toggle_internalformat()

        self.show()

    def on_key_press(self, event):
        if event.key == 'F':
            self.toggle_internalformat()

    def toggle_internalformat(self):
        self._internalformat = (
            (self._internalformat + 1)
            % len(self._internalformats)
        )
        internalformat = self._internalformats[self._internalformat]
        print("Requesting texture internalformat %s" % internalformat)
        self.texture.resize(
            data.shape,
            format='rgb',
            internalformat=internalformat
        )
        self.texture.set_data(data)
        self.program['u_texture'] = self.texture
        self.update()

    def on_resize(self, event):
        gloo.set_viewport(0, 0, *event.physical_size)

    def on_draw(self, event):
        gloo.clear(color=True, depth=True)
        self.program.draw('triangle_strip')

if __name__ == '__main__':
    c = Canvas()
    app.run()