android - libgdx:SpriteBatch，Samsung Android 设备上的 fragment 着色器工作不正确

Question

我正在使用 libgdx 及其 SpriteBatch 类为 Andoid 开发 2D 动态壁纸。这是一 block watch ，所以我需要的只是从 libgdx 绘制多个纹理，将它们旋转到特定角度。

我已经使用 SpriteBatch 类解决了这个问题，一切正常。

但现在我需要在我的场景中添加放大镜效果。任务是以特定比例放大特定区域以模拟真实镜头。

我通过渲染到 FrameBuffer、从 FrameBuffer 获取纹理区域并最终使用 SpriteBatch 使用自定义着色器绘制该区域来解决此问题。

问题:在三星设备上(我在 Galaxy Note N7000 和 Galaxy Tab 10.1 上试过)在放大区域的中心有一个小矩形，大约 16x16 像素，放大率略有增加。抱歉，我现在无法发布屏幕截图，因为我没有三星设备。在其他设备上一切正常，在 HTC Vivid、Acer A500、Google Nexus One 上试过。

我认为，如果三星设备上的 Mali GPU 存在问题，但不知道如何解决。

我已将此问题中的 fragment 着色器代码改编为 SpriteBatch Add Fisheye effect to images at runtime using OpenGL ES这是它:

#ifdef GL_ES
#define LOWP lowp
precision mediump float;
#else
#define LOWP
#endif

varying LOWP vec4 v_color;
varying vec2 v_texCoords;
uniform sampler2D u_texture;

void main() {
vec2 m = vec2(0.622 , 0.4985); // lens center point, note that in live wallpaper center of texture is (0.5,0.5)
float lensSize = 0.045; //diameter of lens
float lensCut = 0.0342; //length of cut lines

vec2 d = v_texCoords - m;
float r = sqrt(dot(d, d)); // distance of pixel from mouse
float cuttop = m.y + lensCut;
float cutbottom = m.y - lensCut; 

vec2 uv;
if (r >= lensSize) {
    uv = v_texCoords;
} else  if ( v_texCoords.y >= cuttop) {
    uv = v_texCoords;
}  else  if (v_texCoords.y <= cutbottom) {
    uv = v_texCoords;
} else {
    uv = m + normalize(d) * asin(r) / (3.14159 * 0.37);
}

gl_FragColor = texture2D(u_texture, uv);
}

顶点着色器默认来自 SpriteBatch 源:

attribute vec4 a_position;
attribute vec4 a_color;
attribute vec2 a_texCoord0;

uniform mat4 u_projTrans;

varying vec4 v_color;
varying vec2 v_texCoords;

void main() {
    v_color = a_color;
    v_texCoords = a_texCoord0;
    gl_Position = u_projTrans * a_position;
}

这是我的render() 方法:

    GL20 gl = Gdx.graphics.getGL20();
    gl.glEnable(GL20.GL_TEXTURE_2D);
    gl.glActiveTexture(GL20.GL_TEXTURE0);

    gl.glClearColor(WallpaperService.bg_red, WallpaperService.bg_green, WallpaperService.bg_blue, 1f);
    gl.glClear(GL20.GL_COLOR_BUFFER_BIT);


    // Creating framebuffer, if it has gone
    if (mFrameBuffer == null) {
        mFrameBuffer = new FrameBuffer(Format.RGBA4444, BG_WIDTH, BG_HEIGHT, true);

        mFrameBufferRegion = new TextureRegion(mFrameBuffer.getColorBufferTexture());
        mFrameBufferRegion.flip(false, true);

    }

    //Camera setting according to background texture
    camera = new OrthographicCamera(BG_WIDTH, BG_HEIGHT);
    camera.position.set(BG_WIDTH / 2, BG_WIDTH / 2, 0);
    camera.update();
    batch.setProjectionMatrix(camera.combined);

    //Rendering scene to framebuffer
    mFrameBuffer.begin();
    batch.begin();
    //main Drawing goes here
    batch.end();

    //Drawing frame to screen with applying shaders for needed effects
    if (mFrameBuffer != null) {
        mFrameBuffer.end();

        camera = new OrthographicCamera(width, height);
        camera.position.set(width / 2, height / 2, 0);
        camera.update();
        batch.setProjectionMatrix(camera.combined);

        batch.begin();
        batch.setShader(null);

        batch.setShader(shader);

        batch.draw(mFrameBufferRegion, width / 2 - (BG_WIDTH / 2) + (MARGIN_BG_LEFT * ratio), height / 2
                - (BG_HEIGHT / 2) + (MARGIN_BG_TOP * ratio), (float) BG_WIDTH / 2, (float) BG_HEIGHT / 2,
                (float) BG_WIDTH, (float) BG_HEIGHT, (float) ratio, (float) ratio, 0f);

        batch.setShader(null);
        batch.end();
    }

Answer 1

我已经设法解决了这个问题。问题出在 Mali gpu 中。Mali 不支持 fragment 着色器中的高精度浮点计算。当中心到点的距离接近于零时 - r 变量变为零。

所以我在计算中添加了常数系数，这就成功了。

这是工作 fragment 着色器:

precision mediump float;

varying lowp vec4 v_color;
varying vec2 v_texCoords;


uniform sampler2D u_texture;

const float PI = 3.14159;
const float koef = 10.0;
void main() {
     vec2 uv;     
    vec2 m = vec2(0.622 , 0.4985); // lens center point, note that in live wallpaper center of texture is (0.5,0.5)
    float lensSize = 0.045; //radius of lens
    float lensCut = 0.0342; //height of cut

    float cuttop = m.y + lensCut;
    float cutbottom = m.y - lensCut;
    float cutleft = m.x-lensSize;
    float cutright = m.x+lensSize;

//don't transform pixels, that aren't in lens area
     if ( v_texCoords.y >= cuttop) {
        uv = v_texCoords;
    }  else  if (v_texCoords.y <= cutbottom) {
        uv = v_texCoords; 
           }  else  if (v_texCoords.x <= cutleft) {
        uv = v_texCoords; 
           }  else  if (v_texCoords.x >= cutright) {
        uv = v_texCoords; 
        } else {
    vec2 p = v_texCoords*koef; //current point 
    vec2 d = p - m*koef; //vector differnce between current point and center point
    float r = distance(m*koef,p); // distance of pixel from center

    if (r/koef >= lensSize) {
        uv = v_texCoords;
      } else {
    uv =m + normalize(d) * asin(r) / (PI*0.37*koef);
    }  
    }

   gl_FragColor = texture2D(u_texture, uv);
}