draw/translate: fix instancing

[mesa.git] / src / gallium / auxiliary / draw / draw_llvm.c

diff --git a/src/gallium/auxiliary/draw/draw_llvm.c b/src/gallium/auxiliary/draw/draw_llvm.c
index 97b463f4ff8bad37c7fcfdf16d16f92bcbf10ab7..f9bcadc6cfa19e27d09c78a568b315b42fb4c2ee 100644 (file)
--- a/src/gallium/auxiliary/draw/draw_llvm.c
+++ b/src/gallium/auxiliary/draw/draw_llvm.c
@@ -674,6 +674,7 @@ generate_vs(struct draw_llvm_variant *variant,
 
 static void
 generate_fetch(struct gallivm_state *gallivm,
+               struct draw_context *draw,
                LLVMValueRef vbuffers_ptr,
                LLVMValueRef *res,
                struct pipe_vertex_element *velem,
@@ -704,10 +705,17 @@ generate_fetch(struct gallivm_state *gallivm,
    struct lp_build_if_state if_ctx;
 
    if (velem->instance_divisor) {
-      /* array index = instance_id / instance_divisor */
-      index = LLVMBuildUDiv(builder, instance_id,
-                            lp_build_const_int32(gallivm, velem->instance_divisor),
-                            "instance_divisor");
+      /* Index is equal to the start instance plus the number of current 
+       * instance divided by the divisor. In this case we compute it as:
+       * index = start_instance + ((instance_id - start_instance) / divisor)
+       */
+      LLVMValueRef current_instance;
+      index = lp_build_const_int32(gallivm, draw->start_instance);
+      current_instance = LLVMBuildSub(builder, instance_id, index, "");
+      current_instance = LLVMBuildUDiv(builder, current_instance,
+                                       lp_build_const_int32(gallivm, velem->instance_divisor),
+                                       "instance_divisor");
+      index = LLVMBuildAdd(builder, index, current_instance, "instance");
    }
 
    stride = lp_build_umul_overflow(gallivm, vb_stride, index, &ofbit);
@@ -1697,7 +1705,7 @@ draw_llvm_generate(struct draw_llvm *llvm, struct draw_llvm_variant *variant,
             LLVMValueRef vb_index =
                lp_build_const_int32(gallivm, velem->vertex_buffer_index);
             LLVMValueRef vb = LLVMBuildGEP(builder, vb_ptr, &vb_index, 1, "");
-            generate_fetch(gallivm, vbuffers_ptr,
+            generate_fetch(gallivm, draw, vbuffers_ptr,
                            &aos_attribs[j][i], velem, vb, true_index,
                            system_values.instance_id);
          }