[原]零基础学习SDL开发之在Android使用SDL2.0渲染PNG图片

在上一篇文章我们知道了如何在android使用SDL2.0来渲染显示一张bmp图，但是如果是一张png或者一张jpg的图，那么还能显示成功么？答案是否定的

我们需要移植SDL_image库来支持除bmp之外的图片格式。

一、移植SDL_image库：

使用如下命令，从SDL Mercurial获取SDL_image的源码：

hg clone https://hg.libsdl.org/SDL_image/

将SDL_image拷贝到在上一篇文章中的android-project\jni\下，将平台相关的代码去掉以及自动自动化相关的文件去掉，保留android相关的代码与文件。

二、在android添加相关的引用：

修改android-project\jni\src\Android.mk，添加相关的引用:

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE := main

SDL_PATH := ../SDL
SDL_IMAGE_PATH := ../SDL2_image

LOCAL_C_INCLUDES := $(LOCAL_PATH)/$(SDL_PATH)/include \
                    $(LOCAL_PATH)/$(SDL_IMAGE_PATH)

# Add your application source files here...
LOCAL_SRC_FILES := $(SDL_PATH)/src/main/android/SDL_android_main.c \
    SDL_lesson.c

LOCAL_SHARED_LIBRARIES := SDL2
LOCAL_SHARED_LIBRARIES += SDL2_image

LOCAL_LDLIBS := -lGLESv1_CM -lGLESv2 -llog

include $(BUILD_SHARED_LIBRARY)

三、代码中引用相关的头文件：

/*
 * SDL_lesson.c
 * Clipping Sprite Sheets
 *  Created on: Aug 12, 2014
 *      Author: clarck
 */
#include <jni.h>
#include "SDL.h"
#include "SDL_image.h"
#include "SDL_logger.h"
#include "SDL_main.h"
#include "SDL_cleanup.h"

//The attributes of the screen
const int SCREEN_WIDTH = ;
const int SCREEN_HEIGHT = ;

struct SDL_Window *window = NULL;
struct SDL_Renderer *render = NULL;

struct SDL_Texture *background = NULL;
struct SDL_Texture *image = NULL;

四、加载图片的部分修改为IMG_LoadTexture:

/*
 * SDL_lesson.c
 * Clipping Sprite Sheets
 *  Created on: Aug 12, 2014
 *      Author: clarck
 */
#include <jni.h>
#include "SDL.h"
#include "SDL_image.h"
#include "SDL_logger.h"
#include "SDL_main.h"
#include "SDL_cleanup.h"

//The attributes of the screen
const int SCREEN_WIDTH = ;
const int SCREEN_HEIGHT = ;

struct SDL_Window *window = NULL;
struct SDL_Renderer *render = NULL;

struct SDL_Texture *background = NULL;
struct SDL_Texture *image = NULL;

/*
 * Loads a image into a texture on the rendering device
 * @param file The image file to load
 * @param ren The renderer to load the texture onto
 * @return the loaded texture, or NULL if something went wrong.
 */
SDL_Texture* loadTexture(const char *file, SDL_Renderer *render) {
    struct SDL_Texture *texture = NULL;

    texture = IMG_LoadTexture(render, file);

    if (texture == NULL) {
        LOGE("SDL_CreateTextureFromSurface failed %s", SDL_GetError());
    } else {
        LOGI("SDL_CreateTextureFromSurface successful.");
    }

    return texture;
}

五、编写主函数：

/*
 * SDL_lesson.c
 * Clipping Sprite Sheets
 *  Created on: Aug 12, 2014
 *      Author: clarck
 */
#include <jni.h>
#include "SDL.h"
#include "SDL_image.h"
#include "SDL_logger.h"
#include "SDL_main.h"
#include "SDL_cleanup.h"

//The attributes of the screen
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;

struct SDL_Window *window = NULL;
struct SDL_Renderer *render = NULL;

struct SDL_Texture *background = NULL;
struct SDL_Texture *image = NULL;

/*
 * Loads a image into a texture on the rendering device
 * @param file The image file to load
 * @param ren The renderer to load the texture onto
 * @return the loaded texture, or NULL if something went wrong.
 */
SDL_Texture* loadTexture(const char *file, SDL_Renderer *render) {
    struct SDL_Texture *texture = NULL;

    texture = IMG_LoadTexture(render, file);

    if (texture == NULL) {
        LOGE("SDL_CreateTextureFromSurface failed %s", SDL_GetError());
    } else {
        LOGI("SDL_CreateTextureFromSurface successful.");
    }

    return texture;
}

/*
 * Draw an SDL_Texture to an SDL_Renderer at position x, y, preserving
 * the texture's width and height
 * @param tex The source texture we want to draw
 * @param ren The renderer we want to draw too
 * @param x The x coordinate to draw too
 * @param y The y coordinate to draw too
 * @param w The width of the texture to draw
 * @param h The height of the texture to draw
 */
void renderTexture(SDL_Texture *tex, SDL_Renderer *ren, SDL_Rect dst,
        SDL_Rect *clip) {
    SDL_RenderCopy(ren, tex, clip, &dst);
}

/*
 * Draw an SDL_Texture to an SDL_Renderer at position x, y, preserving
 * the texture's width and height and taking a clip of the texture if desired
 * If a clip is passed, the clip's width and height will be used instead of the texture's
 * @param tex The source texture we want to draw
 * @param rend The renderer we want to draw too
 * @param x The x coordinate to draw too
 * @param y The y coordinate to draw too
 * @param clip The sub-section of the texture to draw (clipping rect)
 *        default of nullptr draws the entire texture
 */
void renderTexture2(SDL_Texture *tex, SDL_Renderer *ren, int x, int y,
        SDL_Rect *clip) {
    SDL_Rect dst;
    dst.x = x;
    dst.y = y;
    if (clip != NULL) {
        dst.w = clip->w;
        dst.h = clip->h;
    } else {
        SDL_QueryTexture(tex, NULL, NULL, &dst.w, &dst.h);
    }
    renderTexture(tex, ren, dst, clip);
}

int main(int argc, char *argv[]) {
    //char *filefolder = "/storage/sdcard0/";
    char *filefolder = argv[1];
    char *image_temp = "image.png";
    char *background_temp = "background.png";
    LOGI("natvie_SDL %s", filefolder);

    char *background_file = (char*) malloc(
            strlen(filefolder) + strlen(background_temp) + 1);
    strcpy(background_file, filefolder);
    strcat(background_file, background_temp);

    char *image_file = (char*) malloc(
            strlen(filefolder) + strlen(image_temp) + 1);
    strcpy(image_file, filefolder);
    strcat(image_file, image_temp);
    LOGI("natvie_SDL %s", image_file);

    if (SDL_Init(SDL_INIT_EVERYTHING) != 0) {
        LOGE("SDL_Init failed %s", SDL_GetError());
    }

    window = SDL_CreateWindow("lesson5", 100, 100, SCREEN_WIDTH, SCREEN_HEIGHT,
            SDL_WINDOW_SHOWN);
    if (window == NULL) {
        LOGE("SDL_CreateWindow failed %s", SDL_GetError());
    }

    render = SDL_CreateRenderer(window, -1,
            SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
    if (render == NULL) {
        LOGE("SDL_CreateRenderer failed %s", SDL_GetError());
    }

    background = loadTexture(background_file, render);
    image = loadTexture(image_file, render);

    //Clear the window
    SDL_RenderClear(render);

    //Get the width and height from the texture so we know how much to move x,y by
    //to tile it correctly
    int bW, bH;
    SDL_QueryTexture(background, NULL, NULL, &bW, &bH);

    //Draw our image in the center of the window
    //We need the foreground image's width to properly compute the position
    //of it's top left corner so that the image will be centered
    int iW = 100, iH = 100;
    int x = SCREEN_WIDTH / 2 - iW / 2;
    int y = SCREEN_HEIGHT / 2 - iH / 2;

    //Setup the clips for our image
    SDL_Rect clips[4];

    int i;
    for (i = 0; i < 4; i++) {
        clips[i].x = i / 2 * iW;
        clips[i].y = i % 2 * iH;
        clips[i].w = iW;
        clips[i].h = iH;
    }

    //Specify a default clip to start with
    int useClip = 0;

    SDL_Event e;
    int quit = 1;
    while (quit != 0) {
        //Read any events that occured, for now we'll just quit if any event occurs
        while (SDL_PollEvent(&e)) {
            //If user closes the window
            if (e.type == SDL_QUIT) {
                quit = 0;
            }
            //If user presses any key
            if (e.type == SDL_KEYDOWN) {
                switch (e.key.keysym.sym) {
                case SDLK_1:
                    useClip = 0;
                    break;

                case SDLK_2:
                    useClip = 1;
                    break;

                case SDLK_3:
                    useClip = 2;
                    break;

                case SDLK_4:
                    useClip = 3;
                    break;

                case SDLK_ESCAPE:
                    quit = 0;
                    break;

                default:
                    break;
                }
            }
            //If user clicks the mouse
            if (e.type == SDL_MOUSEBUTTONDOWN) {
                quit = 0;
            }
        }

        //Rendering
        SDL_RenderClear(render);

        //We want to tile our background so draw it 4 times
        renderTexture2(background, render, 0, 0, NULL);
        renderTexture2(background, render, bW, 0, NULL);
        renderTexture2(background, render, 0, bH, NULL);
        renderTexture2(background, render, bW, bH, NULL);

        //Draw the image
        renderTexture2(image, render, x, y,  &clips[useClip]);
        SDL_RenderPresent(render);
    }
    //Destroy the various items
    cleanup_texture(image);
    cleanup_render(render);
    cleanup_window(window);
    IMG_Quit();
    SDL_Quit();

    return 0;
}

六、修改SDLActivity，加载SDL2_image库：

  // Load the .so
    static {
        System.loadLibrary("SDL2");
        System.loadLibrary("SDL2_image");
        //System.loadLibrary("SDL2_mixer");
        //System.loadLibrary("SDL2_net");
        //System.loadLibrary("SDL2_ttf");
        System.loadLibrary("main");
    }

运行截图：