CODEWITHSUNDEEP
androidopengl-estexturesglsurfaceview
Nemanja
Nemanja

Reputation: 1535

I need help adding a second texture to glSurfaceView

I used harism's page curl ( Harism, thanx a lot for this excelent library!) for android to develop a commercial application - an electronic magazine.

I wrapped everything that should have been around the app, that is xml - rpc fetching of the magazine pages, caching, loaders, my own bitmap provider, custom gesture event handlers etc...

But, i have a very big problem that no matter how i tried i cannot solve myself.

I need to implement a real book functionality, meaning that when the page is oriented in a landscape mode, i need pairs of pages ( initial screen - left blank, right cover. First flip = left page 1, right page 2. Second flip = left page 3, right page 4... )

I read the info Harism gave to people that asked the same thing on github on the issue they opened concerning this, but that is simply not enough with my limited knowledge of openGL es.

I understand i need to implement a backside texture, but can anyone please be a bit more detailed on this issue? I hit a dead end trying to do it myself and i'm in dire need of help.

If there is ANY need for additional code posting - let me know, i will be more willing to post any / all of the code.

Thanks!

EDIT re- reading it i realized i should have been more detailed. The page that is curling has a texture that is the bitmap of the actual page. At the current setting, the bitmap front and back are rendered separately, but it is the same texture. I need the back one to be the different one.

Some code that does the actual rendering:

/**
 * Draws our mesh.
 */
public synchronized void draw(GL10 gl) {
    // First allocate texture if there is not one yet.
    if (DRAW_TEXTURE && mTextureIds == null) {
        // Generate texture.
        mTextureIds = new int[1];
        gl.glGenTextures(1, mTextureIds, 0);
        // Set texture attributes.
        gl.glBindTexture(GL10.GL_TEXTURE_2D, mTextureIds[0]);
        gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER,
                GL10.GL_LINEAR);
        gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER,
                GL10.GL_LINEAR);
        gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_S,
                GL10.GL_CLAMP_TO_EDGE);
        gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_T,
                GL10.GL_CLAMP_TO_EDGE);
    }
    // If mBitmap != null we have a new texture.
    if (DRAW_TEXTURE && mBitmap != null) {
        gl.glBindTexture(GL10.GL_TEXTURE_2D, mTextureIds[0]);
        GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, mBitmap, 0);
        mBitmap = null;
    }

    if (DRAW_TEXTURE) {
        gl.glBindTexture(GL10.GL_TEXTURE_2D, mTextureIds[0]);
    }

    // Some 'global' settings.
    gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);

    // TODO: Drop shadow drawing is done temporarily here to hide some
    // problems with its calculation.
    if (DRAW_SHADOW) {
        gl.glEnable(GL10.GL_BLEND);
        gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);
        gl.glEnableClientState(GL10.GL_COLOR_ARRAY);
        gl.glColorPointer(4, GL10.GL_FLOAT, 0, mShadowColors);
        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, mShadowVertices);
        gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, mDropShadowCount);
        gl.glDisableClientState(GL10.GL_COLOR_ARRAY);
        gl.glDisable(GL10.GL_BLEND);
    }

    // Enable texture coordinates.
    if (DRAW_TEXTURE) {
        gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
        gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, mTexCoords);
    }
    gl.glVertexPointer(3, GL10.GL_FLOAT, 0, mVertices);

    // Enable color array.
    gl.glEnableClientState(GL10.GL_COLOR_ARRAY);
    gl.glColorPointer(4, GL10.GL_FLOAT, 0, mColors);

    // Draw blank / 'white' front facing vertices.
    gl.glDisable(GL10.GL_TEXTURE_2D);
    gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, mVerticesCountFront);
    // Draw front facing texture.
    // TODO: Decide whether it's really needed to have alpha blending for
    // front facing texture. If not, GL_BLEND isn't needed, possibly
    // increasing performance. The heck, is it needed at all?
    if (DRAW_TEXTURE) {
        gl.glEnable(GL10.GL_BLEND);
        gl.glEnable(GL10.GL_TEXTURE_2D);
        gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);
        gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, mVerticesCountFront);
        gl.glDisable(GL10.GL_TEXTURE_2D);
        gl.glDisable(GL10.GL_BLEND);
    }
    int backStartIdx = Math.max(0, mVerticesCountFront - 2);
    int backCount = mVerticesCountFront + mVerticesCountBack - backStartIdx;
    // Draw blank / 'white' back facing vertices.
    gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, backStartIdx, backCount);
    // Draw back facing texture.
    if (DRAW_TEXTURE) {
        gl.glEnable(GL10.GL_BLEND);
        gl.glEnable(GL10.GL_TEXTURE_2D);
        gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);
        gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, backStartIdx, backCount);
        gl.glDisable(GL10.GL_TEXTURE_2D);
        gl.glDisable(GL10.GL_BLEND);
    }

    // Disable textures and color array.
    gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
    gl.glDisableClientState(GL10.GL_COLOR_ARRAY);

    if (DRAW_POLYGON_OUTLINES) {
        gl.glEnable(GL10.GL_BLEND);
        gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);
        gl.glLineWidth(1.0f);
        gl.glColor4f(0.5f, 0.5f, 1.0f, 1.0f);
        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, mVertices);
        gl.glDrawArrays(GL10.GL_LINE_STRIP, 0, mVerticesCountFront);
        gl.glDisable(GL10.GL_BLEND);
    }

    if (DRAW_CURL_POSITION) {
        gl.glEnable(GL10.GL_BLEND);
        gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);
        gl.glLineWidth(1.0f);
        gl.glColor4f(1.0f, 0.5f, 0.5f, 1.0f);
        gl.glVertexPointer(2, GL10.GL_FLOAT, 0, mCurlPositionLines);
        gl.glDrawArrays(GL10.GL_LINES, 0, mCurlPositionLinesCount * 2);
        gl.glDisable(GL10.GL_BLEND);
    }

    if (DRAW_SHADOW) {
        gl.glEnable(GL10.GL_BLEND);
        gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);
        gl.glEnableClientState(GL10.GL_COLOR_ARRAY);
        gl.glColorPointer(4, GL10.GL_FLOAT, 0, mShadowColors);
        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, mShadowVertices);
        gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, mDropShadowCount,
                mSelfShadowCount);
        gl.glDisableClientState(GL10.GL_COLOR_ARRAY);
        gl.glDisable(GL10.GL_BLEND);
    }

    gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
}

I suppose i should tamper with :

// Draw back facing texture.
if (DRAW_TEXTURE) {
    gl.glEnable(GL10.GL_BLEND);
    gl.glEnable(GL10.GL_TEXTURE_2D);
    gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);
    gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, backStartIdx, backCount);
    gl.glDisable(GL10.GL_TEXTURE_2D);
    gl.glDisable(GL10.GL_BLEND);
}

And provide it with a sepparate bitmap, but i don't know how to do this.

Thanks again

EDIT: I started a mega- bounty, i really need this answered... :)

Upvotes: 3

Views: 1200

Answers (1)

Macarse
Macarse

Reputation: 93143

My openGL knowledge is also limited but I had a similar issue in the past. To have two textures you will need, at least, to modify this line:

gl.glGenTextures(2, mTextureIds, 0);

Here you have an example of how to use more than one texture.

Upvotes: 1

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