godot/drivers/gles2/shaders/ssao_minify.glsl

/* clang-format off */
[vertex]

layout(location = 0) in highp vec4 vertex_attrib;
/* clang-format on */

void main() {

	gl_Position = vertex_attrib;
}

/* clang-format off */
[fragment]

#ifdef MINIFY_START

#define SDEPTH_TYPE highp sampler2D
uniform float camera_z_far;
uniform float camera_z_near;
/* clang-format on */

#else

#define SDEPTH_TYPE mediump usampler2D

#endif

uniform SDEPTH_TYPE source_depth; //texunit:0

uniform ivec2 from_size;
uniform int source_mipmap;

layout(location = 0) out mediump uint depth;

void main() {

	ivec2 ssP = ivec2(gl_FragCoord.xy);

	// Rotated grid subsampling to avoid XY directional bias or Z precision bias while downsampling.
	// On DX9, the bit-and can be implemented with floating-point modulo

#ifdef MINIFY_START
	float fdepth = texelFetch(source_depth, clamp(ssP * 2 + ivec2(ssP.y & 1, ssP.x & 1), ivec2(0), from_size - ivec2(1)), source_mipmap).r;
	fdepth = fdepth * 2.0 - 1.0;
#ifdef USE_ORTHOGONAL_PROJECTION
	fdepth = ((fdepth + (camera_z_far + camera_z_near) / (camera_z_far - camera_z_near)) * (camera_z_far - camera_z_near)) / 2.0;
#else
	fdepth = 2.0 * camera_z_near * camera_z_far / (camera_z_far + camera_z_near - fdepth * (camera_z_far - camera_z_near));
#endif
	fdepth /= camera_z_far;
	depth = uint(clamp(fdepth * 65535.0, 0.0, 65535.0));

#else
	depth = texelFetch(source_depth, clamp(ssP * 2 + ivec2(ssP.y & 1, ssP.x & 1), ivec2(0), from_size - ivec2(1)), source_mipmap).r;
#endif
}