CODEWITHSUNDEEP
iosopengl-esrenderingglsl
victor.t
victor.t

Reputation: 454

Avoiding texture switching (openGL es 2.0)

I'm working on small 2d rendering engine for IOS. I want to render many sprites that are located in different textures. Now that sounds simple... Just render all sprites that belong to same texture and move to next ... But how to handle overlapping of primitives that have different textures?

problem

I want to render them in exact same way as on the picture (overlapped). That means I need to switch texture three times. What if I have hundreeds of such mixed sprites? To avoid texture switching on client and render all sprites in one shot. I'm using following code in fragment shader:

if(txt >= 0.5)
    gl_FragColor = texture2D(texture1, texCoords)* clr;

if (txt >= 1.5)
    gl_FragColor = texture2D(texture2, texCoords)* clr;

if (txt >= 2.5)
    gl_FragColor= texture2D(texture3, texCoords)* clr;

if (txt >= 3.5)
    gl_FragColor = texture2D(texture4, texCoords)* clr;

if (txt >= 4.5)
    gl_FragColor = texture2D(texture5, texCoords) * clr;

Because of dynamic branching I have performance issues running on device. Is there better solution?

Upvotes: 2

Views: 761

Answers (1)

Nicol Bolas
Nicol Bolas

Reputation: 474136

Assuming you have evidence of a real performance issue (and you shouldn't bother with this unless you do), the solution is quite easy: use your depth buffer.

Use an orthographic projection so that sprites don't get bigger/smaller when they move forward. Give each sprite a depth value, and let the depth test remove unwanted parts of sprites.

Upvotes: 1

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