change grid shader primitive to line from triangle

src/renderer_sdlgpu.c

@@ -733,29 +733,14 @@ bool renderer_init(SDL_Window *window_) {
             .fragment_shader = fragment_shader,
 
             .vertex_input_state = {
-                .vertex_buffer_descriptions = (SDL_GPUVertexBufferDescription[]){
-                    {
-                        .slot       = 0,
-                        .pitch      = 20,
-                        .input_rate = SDL_GPU_VERTEXINPUTRATE_VERTEX,
+                .vertex_buffer_descriptions = (SDL_GPUVertexBufferDescription[]){},
+                .num_vertex_buffers = 0,
 
-                        .instance_step_rate = 0,
-                    },
-                },
-                .num_vertex_buffers = 1,
-
-                .vertex_attributes = (SDL_GPUVertexAttribute[]){
-                    {
-                        .location    = 0,
-                        .buffer_slot = 0,
-                        .format      = SDL_GPU_VERTEXELEMENTFORMAT_FLOAT3,
-                        .offset      = 0,
-                    },
-                },
-                .num_vertex_attributes = 1,
+                .vertex_attributes = (SDL_GPUVertexAttribute[]){},
+                .num_vertex_attributes = 0,
             },
 
-            .primitive_type = SDL_GPU_PRIMITIVETYPE_TRIANGLELIST,
+            .primitive_type = SDL_GPU_PRIMITIVETYPE_LINELIST,
 
             .rasterizer_state = {
                 .fill_mode  = SDL_GPU_FILLMODE_FILL,
@@ -824,6 +809,10 @@ bool renderer_init(SDL_Window *window_) {
         SDL_ReleaseGPUShader(device, fragment_shader);
     }
 
+    for (int i = 0; i < R_SHADER_COUNT; i++) {
+        SDL_assert(shaders[i]);
+    }
+
     transfer_buffer = SDL_CreateGPUTransferBuffer(device, &(SDL_GPUTransferBufferCreateInfo){
         .usage = SDL_GPU_TRANSFERBUFFERUSAGE_UPLOAD,
         .size  = 64 * 1024,