我有一个 kivy 应用程序，我希望在特定 RenderContext 上绘制的所有内容都应用着色器后处理效果（类似于文档中 kivy-examples 中的 EffectWidget 示例中演示的效果）。
在worldWidget 的构造函数中，我创建了RenderContext
self.prc = RenderContext()
设置它的投影矩阵（这有效）
self.prc['projection_mat'] = proj_mat
然后尝试将其片段着色器设置为默认片段着色器的最小副本，该副本应该使所有内容变为不透明的十分之一（基本上使屏幕变暗）。
self.prc.shader.fs = """
#ifdef GL_ES
precision highp float;
#endif
/* Outputs from the vertex shader */
varying vec4 frag_color;
varying vec2 tex_coord0;
/* uniform texture samplers */
uniform sampler2D texture0;
void main (void){
gl_FragColor = 0.1*frag_color * texture2D(texture0, tex_coord0);
}
"""
如果此着色器的代码不正确，则程序不会运行，并抱怨着色器编译错误，这表明正在编译着色器。但是，我看不到着色器的任何效果。渲染到的所有内容都prc被绘制，但具有正常的不透明度。我究竟做错了什么？谢谢你的时间！
编辑！
我被要求提供一个完整的可运行示例。下面的程序绘制两个矩形。左边的 Rectangle 有自己的 RenderContext 并且不受灰度后处理效果的影响（它被绘制为红色）。右侧的 Rectangle 没有自己的 RenderContext，它正确地受到后处理效果的影响。
这是代码：
from kivy.app import App
from kivy.uix.widget import Widget
from kivy.uix.floatlayout import FloatLayout
from kivy.graphics import *
from kivy.graphics.opengl import *
from kivy.graphics.shader import *
from kivy.core.window import Window
from kivy.graphics.transformation import Matrix
from kivy.logger import Logger
class World(Widget) :
def __init__(self, **kwargs):
Logger.debug('world.init()')
# Parent RenderContext for subsuming all other render contexts
self.prc=RenderContext()
proj_mat = Matrix()
proj_mat.look_at(0.,0.,1., # eye position coords
0.,0.,0., # looking at these coords
0,1.,0) # a vector that points up
if Window.height > Window.width :
self.xRadius = float(Window.width)/Window.height
self.yRadius = 1.0
proj_mat.scale(1.0/self.xRadius,1.0,1.0)
else :
self.xRadius = 1.0
self.yRadius = float(Window.height)/Window.width
proj_mat.scale(1.0,1.0/self.yRadius,1.0)
self.prc['projection_mat'] = proj_mat
## an effect shader used to make objects monochromatic (grayscale)
self.prc.shader.fs = """
#ifdef GL_ES
precision highp float;
#endif
/* Outputs from the vertex shader */
varying vec4 frag_color;
varying vec2 vTexCoords0;
/* uniform texture samplers */
uniform sampler2D texture0;
uniform vec2 resolution;
uniform float time;
void main() {
vec4 rgb = texture2D(texture0, vTexCoords0);
float c = (rgb.x + rgb.y + rgb.z) * 0.3333;
gl_FragColor = vec4(c, c, c, 1.0);
}
"""
if not self.prc.shader.success :
raise Exception('Effect shader compile failed.')
self.canvas = self.prc
## Left Rectangle drawn with its own RenderContext
## this is not affected by the effect shader (if it were, it would be drawn as white)
## but it is affected by the parent's projection matrix
self.spriteRC = RenderContext(use_parent_projection=True)
self.spriteRC.add(Color(1,0,0,1))
self.spriteRC.add(Rectangle(pos=(-0.25,0.0),size=(0.1,0.1)))
## Right Rectangle object drawn directly to the canvas
## this **is** affected by the effect shader
self.canvas.add(Color(1,0,0,1))
self.canvas.add(Rectangle(pos=(0.25,0),size=(0.1,0.1)))
self.canvas.add(self.spriteRC)
super(World, self).__init__(**kwargs)
class GameApp(App):
def build(self):
w = World()
fl = FloatLayout()
fl.add_widget(w)
return fl
if __name__ == '__main__':
GameApp().run()