FPGA 实现任意角度图像旋转：原理与流水线设计

2.4 第二级流水线

开始计算旋转公式。以中心点为原点 (0,0)，覆盖四个象限。公式组合后右移 14 位处理定点数精度。

reg signed [12:0] x_cos;
reg signed [12:0] y_sin;
reg signed [12:0] y_cos;
reg signed [12:0] x_sin;

assign row_abs = row_size;
assign col_abs = col_size;
assign row1 = row_abs >> 1;
assign col1 = col_abs >> 1;

always @(posedge clk_i, negedge rstn_i) begin
    if (!rstn_i) x_cos <= 'd0;
    else if(r_rotate_valid_1d) x_cos <= ((hcnt - col1 ) * cosout) >>>14;
    else x_cos <= x_cos;
end

always @(posedge clk_i, negedge rstn_i) begin
    if (!rstn_i) y_sin <= 'd0;
    else if(r_rotate_valid_1d) y_sin <= ((vcnt-row1 ) * sinout) >>>14;
    else y_sin <= y_sin;
end

always @(posedge clk_i, negedge rstn_i) begin
    if (!rstn_i) y_cos <= 'd0;
    else if(r_rotate_valid_1d) y_cos <= ((vcnt - row1 ) * cosout) >>>14;
    else y_cos <= y_cos;
end

always @(posedge clk_i, negedge rstn_i) begin
    if (!rstn_i) x_sin <= 'd0;
    else if(r_rotate_valid_1d) x_sin <= ((hcnt - col1 ) * sinout) >>>14;
    else x_sin <= x_sin;
end

2.5 第三级流水线

将旋转后的中心坐标转换回屏幕坐标系。流程为：原始坐标 -> 中心坐标系 -> 应用旋转公式 -> 旋转后中心坐标 -> 屏幕坐标系。

always @(posedge clk_i, negedge rstn_i) begin
    if (!rstn_i) r_rotate_valid_2d <= 'd0;
    else r_rotate_valid_2d <= r_rotate_valid_1d;
end

always @(posedge clk_i, negedge rstn_i) begin
    if (!rstn_i) hcnt_rotate <= 'd0;
    else if(r_rotate_valid_2d==1'b1)
        hcnt_rotate <= x_cos - y_sin + (COL>>1);
    else hcnt_rotate <= 'd0;
end

always @(posedge clk_i, negedge rstn_i) begin
    if (!rstn_i) vcnt_rotate <= 'd0;
    else if(r_rotate_valid_2d==1'b1)
        vcnt_rotate <= y_cos + x_sin + (ROW>>1);
    else vcnt_rotate <= 'd0;
end

2.6 第四级流水线

判断旋转坐标是否在原图像范围内，生成 ROM 地址。data_cnt 计数器防止地址溢出或重复读取。ROM 读出数据延迟一个时钟，此处做对齐处理。

always @(posedge clk_i, negedge rstn_i) begin
    if (!rstn_i) r_rotate_valid_3d <= 'd0;
    else r_rotate_valid_3d <= r_rotate_valid_2d;
end

always @(posedge clk_i, negedge rstn_i) begin
    if (!rstn_i) begin
        rden <= 'd0;
        addra <= 'd0;
    end else if(r_rotate_valid_3d==1'b1) begin
        if((hcnt_rotate>='d0)&&(hcnt_rotate<COL)&&(vcnt_rotate>='d0)&&(vcnt_rotate<ROW)&&data_cnt<ROW*COL) begin
            rden <= 1'b1;
            addra<= COL*vcnt_rotate + hcnt_rotate;
        end else begin
            rden <= 1'b0;
            addra<= 'd0;
        end
    end else begin
        rden <= 1'b0;
        addra <= 'd0;
    end
end

always @(posedge clk_i, negedge rstn_i) begin
    if (!rstn_i) data_cnt <= 'd0;
    else if (data_cnt == ROW*COL - 1) data_cnt <= 'd0;
    else if (r_rotate_valid_3d && (hcnt_rotate>='d0)&&(hcnt_rotate<COL)&&(vcnt_rotate>='d0)&&(vcnt_rotate<ROW))
        data_cnt <= data_cnt + 'd1;
end

img_mem_gen img_mem_gen_inst (.address(addra), .clock(clk_i), .rden(rden), .q(rom_data));

3. 仿真结果

测试不同角度的旋转效果，包括逆时针 30°、顺时针 30° 及大角度 228° 等。

结果显示任意角度、任意方向的旋转均能正常实现。

4. 结语

本方案基于通用 LCD 时序逻辑编写，重点在于旋转算法的硬件实现。代码架构采用模块化流水线设计，便于后续优化与移植。实际项目中需结合具体资源情况调整时序与语法规范。