How to implement bgl.glScissor with using gpu module?

Question

As you know, bgl module has been deprecated and will be deleted in the future Blender release. So, I'm tackling to change my old code to use gpu module.

My old code uses bgl.glScissor to clip the target rendered by blf and blf module. However, I could not find the way to implement same function (like bgl.glScissor) with gpu module.

Is there any way to realize bgl.glScissor with gpu module?

Answer 1

The term "scissor" does not appear in the docs, so I assume a direct equivalent does not exist.

What you could do instead is use a shader that discards fragments outside of the scissor rectangle. The rectangle boundaries would be passed with a uniform.

Here's the second example from the gpu module docs modified to do this. Added lines have been marked with a #.

import bpy
import gpu
from gpu_extras.batch import batch_for_shader


vert_out = gpu.types.GPUStageInterfaceInfo("my_interface")
vert_out.smooth('VEC3', "pos")

shader_info = gpu.types.GPUShaderCreateInfo()
shader_info.push_constant('MAT4', "viewProjectionMatrix")
shader_info.push_constant('FLOAT', "brightness")
shader_info.push_constant('VEC4', "scissorRect")                 #
shader_info.vertex_in(0, 'VEC3', "position")
shader_info.vertex_out(vert_out)
shader_info.fragment_out(0, 'VEC4', "FragColor")

shader_info.vertex_source(
    "void main()"
    "{"
    "  pos = position;"
    "  gl_Position = viewProjectionMatrix * vec4(position, 1.0f);"
    "}"
)

shader_info.fragment_source(
    "void main()"
    "{"
    "  if ("                                                     #
    "    gl_FragCoord.x < scissorRect.x || "                     #
    "    gl_FragCoord.x > scissorRect.z || "                     #
    "    gl_FragCoord.y < scissorRect.y || "                     #
    "    gl_FragCoord.y > scissorRect.w "                        #
    "  ) discard;"                                               #
    "  FragColor = vec4(pos * brightness, 1.0);"
    "}"
)

shader = gpu.shader.create_from_info(shader_info)
del vert_out
del shader_info

coords = [(1, 1, 1), (2, 0, 0), (-2, -1, 3)]
batch = batch_for_shader(shader, 'TRIS', {"position": coords})


def draw():
    matrix = bpy.context.region_data.perspective_matrix
    shader.uniform_float("viewProjectionMatrix", matrix)
    shader.uniform_float("brightness", 0.5)
    shader.uniform_float("scissorRect", [100, 100, 300, 300])    #
    batch.draw(shader)


bpy.types.SpaceView3D.draw_handler_add(draw, (), 'WINDOW', 'POST_VIEW')

Answer 2

As of Blender 3.6, the gpu module now has gpu.state.scissor_set and gpu.state.scissor_test_set.