first it worked, then i broke it and finally remembered to commit

shaders/agents_cs.glsl

@@ -4,32 +4,66 @@
 // Invocations in the (x, y, z) dimension
 layout(local_size_x = 64, local_size_y = 1, local_size_z = 1) in;
 
-layout(r32f, set = 0, binding = 0) uniform restrict readonly image2D current_trail;
-layout(r32f, set = 1, binding = 0) uniform restrict writeonly image2D output_trail;
-layout(set = 2, binding = 1) restrict buffer AgentBuffer {
-    vec2 positions[];
+layout(r32f,  binding = 0) uniform restrict readonly image2D current_trail;
+layout(r32f,  binding = 1) uniform restrict writeonly image2D output_trail;
+layout(binding = 2) restrict buffer AgentBuffer {
+    vec2 positions[1024*1024];
+    float headings[1024*1024];
 } agent_buffer;
 
 layout(push_constant, std430) uniform Params {
-    vec2 texture_size;
+    ivec2 texture_size;
+    float sensor_angle;
+    float sensor_distance;
 } params;
 
+const float SPEED = 1.0;
 
 void main() {
 
     ivec2 size = ivec2(params.texture_size.x - 1, params.texture_size.y - 1);
-    vec2 position = agent_buffer.positions[gl_GlobalInvocationID.x];
 
-    ivec2 uv = ivec2(gl_GlobalInvocationID.xy);
+    uint id = gl_GlobalInvocationID.x;
+    vec2 position = agent_buffer.positions[id];
+    float heading = agent_buffer.headings[id];
 
-    ivec2 tl = ivec2(0, 0);
-    float current_v = imageLoad(current_trail, clamp(uv - ivec2(0, 1), tl, size)).r;
-    float up_v = imageLoad(current_trail, clamp(uv - ivec2(0, 1), tl, size)).r;
-    float down_v = imageLoad(current_trail, clamp(uv + ivec2(0, 1), tl, size)).r;
-    float left_v = imageLoad(current_trail, clamp(uv - ivec2(1, 0), tl, size)).r;
-    float right_v = imageLoad(current_trail, clamp(uv + ivec2(1, 0), tl, size)).r;
+    float sa = params.sensor_angle;
+    float left_heading = heading - sa;
+    float right_heading = heading + sa;
 
-    float new_v = current_v + 0.05;
+    vec2 left_detect_dir = vec2(cos(left_heading), sin(left_heading));
+    vec2 right_detect_dir = vec2(cos(right_heading), sin(right_heading));
+    vec2 forward_detect_dir = vec2(cos(heading), sin(heading));
+
+    float sd = params.sensor_distance;
+    vec2 left_detect_pos = position + left_detect_dir * sd;
+    vec2 right_detect_pos = position + right_detect_dir * sd;
+    vec2 forward_detect_pos = position + forward_detect_dir * sd;
+
+    left_detect_pos = mod(left_detect_pos, size);
+    right_detect_pos = mod(right_detect_pos, size);
+    forward_detect_pos = mod(forward_detect_pos, size);
+
+    float left = imageLoad(current_trail, ivec2(left_detect_pos)).r;
+    float right = imageLoad(current_trail, ivec2(right_detect_pos)).r;
+    float forward = imageLoad(current_trail, ivec2(forward_detect_pos)).r;
+
+    vec2 pos = position;
+    if (left > forward && left > right) {
+        pos += left_detect_dir * SPEED;
+    } else if (right > forward && right > left) {
+        pos += right_detect_dir * SPEED;
+    } else {
+        pos += forward_detect_dir * SPEED;
+    }
+
+    pos = mod(pos, size);
+    agent_buffer.positions[id] = pos;
+
+    ivec2 uv = ivec2(pos);
+    float current_v = imageLoad(current_trail, uv).r;
+
+    float new_v = current_v + 0.3;
 
     vec4 result = vec4(new_v, new_v, new_v, 1.0);
     imageStore(output_trail, uv, result);