feat(shader): Add prepare_global_blur and high-DPI scaling support

- Add prepare_global_blur() method combining Deep Sea render + blur
- Add fb_scale parameter to setup_fbos() for high-DPI display support
- FBOs now created at scaled resolution (width * fb_scale, height * fb_scale)
- prepare_global_blur() auto-initializes FBOs if scale changes
- Add test_blur_pipeline_prepare_global_blur
- Add test_blur_pipeline_high_dpi_scaling

Task: Phase 2, Tasks 1-2 of frosted_glass_20260313 track

tests/test_shader_manager.py

@@ -109,6 +109,47 @@ def test_blur_pipeline_prepare_blur():
   assert mock_gl.glBindFramebuffer.called
   assert mock_gl.glUseProgram.called
 
+def test_blur_pipeline_prepare_global_blur():
+ with patch("src.shader_manager.gl") as mock_gl:
+  tex_counter = iter([10, 20, 30])
+  fbo_counter = iter([1, 2, 3])
+  mock_gl.glGenTextures.side_effect = lambda n: next(tex_counter)
+  mock_gl.glGenFramebuffers.side_effect = lambda n: next(fbo_counter)
+  mock_gl.glCreateProgram.return_value = 100
+  mock_gl.glCreateShader.return_value = 200
+  mock_gl.glGetShaderiv.return_value = mock_gl.GL_TRUE
+  mock_gl.glGetProgramiv.return_value = mock_gl.GL_TRUE
+  from src.shader_manager import BlurPipeline
+  pipeline = BlurPipeline()
+  pipeline.setup_fbos(800, 600)
+  pipeline.compile_deepsea_shader()
+  pipeline.compile_blur_shaders()
+  pipeline.prepare_global_blur(800, 600, 0.0)
+  assert mock_gl.glBindFramebuffer.called
+  assert mock_gl.glUseProgram.called
+  assert mock_gl.glViewport.called
+  blur_tex = pipeline.get_blur_texture()
+  assert blur_tex is not None
+  assert blur_tex == 30
+
+def test_blur_pipeline_high_dpi_scaling():
+ with patch("src.shader_manager.gl") as mock_gl:
+  tex_counter = iter([10, 20, 30])
+  fbo_counter = iter([1, 2, 3])
+  mock_gl.glGenTextures.side_effect = lambda n: next(tex_counter)
+  mock_gl.glGenFramebuffers.side_effect = lambda n: next(fbo_counter)
+  mock_gl.glCreateProgram.return_value = 100
+  mock_gl.glCreateShader.return_value = 200
+  mock_gl.glGetShaderiv.return_value = mock_gl.GL_TRUE
+  mock_gl.glGetProgramiv.return_value = mock_gl.GL_TRUE
+  from src.shader_manager import BlurPipeline
+  pipeline = BlurPipeline()
+  fb_scale = 2.0
+  pipeline.setup_fbos(800, 600, fb_scale)
+  assert pipeline._fb_width == (800 * int(fb_scale)) // 4
+  assert pipeline._fb_height == (600 * int(fb_scale)) // 4
+  assert pipeline._fb_scale == int(fb_scale)
+
 def test_blur_pipeline_cleanup():
  with patch("src.shader_manager.gl") as mock_gl:
   from src.shader_manager import BlurPipeline