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 = 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;
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 = 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;
}
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：
